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GENOMAS E GENÉTICA VIRAL
Biomedicina Interdisciplinar
�1
Virology breakthrough in the 1950’s:
O código genético viral é composto por ácidos nucleicos
Hershey-Chase 
experiment with 
phage T4
©Principles of Virology, ASM Press
Fraenkel-Conrat’s work with TMV
�2
Alfred Hershey & Martha Chase, 1952
©Principles of Virology, ASM Press
�3
A grande surpresa: milhares de vírions 
diferentes, indicando uma complexidade 
infinita de infecções
Entretanto, um número finito de 
genomas virais
�4
Esquema geral de infecção26 Chapter 2
Cytoplasm
Attachment and entry
Translation
Release
VP0 VP2 VP1
P1 P2 P3
3B(VPg)
Endoplasmic
reticulum
Membrane
vesicle
Genome
replication
Assembly
Nucleus
Figure 2.1 The viral infec-
tious cycle. The infectious cycle 
of poliovirus is shown as an exam-
ple, illustrating the steps common 
to all viral life cycles: attachment 
and entry, translation, genome 
replication, assembly, and release. 
See Appendix, Figures 21 and 22 
for explanation of abbreviations. 
Nucleus
Nuclear envelope:
Cytoplasm
Cytoskeleton:
Nuclear pore complex
Outer nuclear membrane
Inner nuclear membrane
Microtubule
Intermediate filament
Actin filament bundle
Rough endoplasmic reticulumRibosomeGolgi apparatus
Plasma
membrane
Transport
vesicles
Extracellular matrixLysosomeEndosome
Coated pit
Mitochondrion
Nuclear lamina
Figure 2.2 The mammalian cell. Illustrated schematically are the nucleus, the major membrane-bound 
compartments of the cytoplasm, and components of the cytoskeleton that play important roles in virus 
reproduction. A small part of the cytoplasm is magnified, showing the crowded contents. The figure is not 
drawn to scale.
ASM_POV4e_Vol1_Ch02.indd 26ASM_POV4e_Vol1_Ch02.indd 26 7/22/15 12:13 PM7/22/15 12:13 PM
 The Infectious Cycle 31
anchored proteins are bound to the plasma membrane lipid 
bilayer by interacting either with integral membrane proteins 
or with the charged sugars of the glycolipids. Fibronectin, a 
protein in the extracellular matrix that binds to integrins 
(Fig. 2.4), is an example. 
 Entering Cells 
 Viral infection is initiated by a collision between the virus 
particle and the cell, a process that is governed by chance. 
Consequently, a higher concentration of virus particles 
increases the probability of infection. However, a virion may 
not infect every cell it encounters; it must first come in con-
tact with the cells and tissues to which it can bind. Such cells 
are normally recognized by means of a specific interaction of 
a virus particle with a cell surface receptor. These molecules 
do not exist for the benefit of viruses: they all have cellular 
functions, and viruses have evolved to bind them for cell 
entry. Virus-receptor interactions can be either promiscu-
ous or highly selective, depending on the virus and the dis-
tribution of the cell receptor. The presence of such receptors 
determines whether the cell will be susceptible to the virus. 
However, whether a cell is permissive for the reproduction of 
a particular virus depends on other, intracellular components 
found only in certain cell types. Cells must be both susceptible 
 and permissive if an infection is to be successful. 
 Viruses have no intrinsic means of locomotion, but their 
small size facilitates diff usion driven by Brownian motion. 
Propagation of viruses is dependent on essentially random 
encounters with potential hosts and host cells. Features 
that increase the probability of favorable encounters are 
very important. In particular, viral propagation is critically 
dependent on the production of large numbers of progeny 
virus particles with surfaces composed of many copies of 
structures that enable the attachment of virus particles to 
susceptible cells. 
 Successful entry of a virus into a host cell requires 
traversal of the plasma membrane and in some cases the 
nuclear membrane. Th e virus particle must be partially or 
completely disassembled, and the nucleic acid must be tar-
geted to the correct cellular compartment. Th ese are not 
simple processes. Furthermore, virus particles or critical 
subassemblies are brought across such barriers by specifi c 
transport pathways. To survive in the extracellular envi-
ronment, the viral genome must be encapsidated in a pro-
tective coat that shields viral nucleic acid from the variety 
of potentially harsh conditions that may be met during 
transit from one host cell or organism to another. For 
example, UV irradiation (from sunlight), extremes of pH 
(in the gastrointestinal tract), dehydration (in the air), and 
enzymatic attack (in body fl uids) are all capable of damag-
ing viral nucleic acids. However, once in the host cell, the 
protective structures must become suffi ciently unstable to 
release the genome. Virus particles cannot be viewed only 
as passive vehicles: they must be able to undergo structural 
transformations that are important for attachment and entry 
into a new host cell and for the subsequent disassembly 
required for viral replication. 
 Making Viral RNA 
 Although the genomes of viruses come in a number of con-
figurations, they share a common requirement: they must 
be efficiently copied into mRNAs for the synthesis of viral 
proteins and progeny genomes for assembly. The synthe-
sis of RNA molecules in cells infected with RNA viruses is 
a unique process that has no counterpart in the cell. With 
the exception of retroviruses, all RNA viruses encode an 
RNA-dependent RNA polymerase to catalyze the synthesis 
of mRNAs and genomes. For the majority of DNA viruses 
and retroviruses, synthesis of viral mRNA is accomplished 
by RNA polymerase II, the enzyme that produces cellular 
mRNA. Much of our current understanding of the mech-
anisms of cellular transcription comes from study of the 
transcription of viral templates. 
 Making Viral Proteins 
 Because viruses are parasites of translation, all viral 
mRNAs must be translated by the host’s cytoplasmic 
protein-synthesizing machinery (see Chapter 11). However, 
viral infection often results in modification of the host’s 
translational apparatus so that viral mRNAs are translated 
selectively. The study of such modifications has revealed a 
great deal about mechanisms of protein synthesis. Analysis 
of viral translation has also revealed new strategies, such as 
internal ribosome binding and leaky scanning, that have been 
subsequently found to occur in uninfected cells. 
 Making Viral Genomes 
 Many viral genomes are copied by the cell’s synthetic 
machinery in cooperation with viral proteins (see Chapters 6 
through 9). The cell provides nucleotide substrates, energy, 
enzymes, and other proteins. Transport systems are required 
because the cell is compartmentalized: essential components 
might be found only in the nucleus, the cytoplasm, or cellular 
membranes. Study of the mechanisms of viral genome 
 replication has established fundamental principles of cell 
biology and nucleic acid synthesis. 
 Forming Progeny Virus Particles 
 The various components of a virus particle—the nucleic 
acid genome, capsid protein(s), and in some cases enve-
lope proteins—are often synthesized in different cellular 
compartments. Their trafficking through and among the 
ASM_POV4e_Vol1_Ch02.indd 31ASM_POV4e_Vol1_Ch02.indd 31 7/22/15 12:13 PM7/22/15 12:13 PM
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Dogma Central da Biologia
Os genomas virais devem fazer 
mRNA que consiga ser lido pelos 
ribossomos do hospedeiro 
Todos os vírus do planeta seguem esta regra
Fato rápido
�7
David Baltimore (Nobel laureate)
Classificação de Baltimore
VII
©Principles of Virology, ASM Press�8
Definições
• Para tradução, o mRNA é sempre positivo (+) 
• DNA que é equivalente ao mRNA 
também é positivo (+)
• As fitas de RNA e DNA complementares a fitas 
positivas (+) são negativas (-)
• Nem todo RNA (+) é mRNA!
VII
©Principles of Virology, ASM Press�9
Sabendo a natureza do genoma viral, é possíveldeduzir as etapas essenciais que devem ocorrer 
dentro da célula para a produção do mRNA
A elegância do Sistema de Baltimore
VII
©Principles of Virology, ASM Press�10
• dsDNA
• dsDNA parcial
• ssDNA
• dsRNA
• ss (+) RNA
• ss (-) RNA
• ss (+) RNA com intermediário de DNA
As sete classes de genomas virais
©Principles of Virology, ASM Press
VII
�11
SOCRATIVE
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Nome da Sala: PERES2018 
Por que o mRNA é colocado no centro da Classificação de Baltimore? 
a) Porque todas as partículas virais possuem mRNA. 
b) Não há razão específica. 
c) Porque todos os genomas virais são de RNA. 
d) Porque um mRNA deve ser produzido a partir de todos os genomas virais. 
e) Porque os vírus com genoma ssRNA sempre são positivos (+). 
�12
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•
•
•
•
•
•
•
•
•
•
•
Linear
Circular 
Segmentado 
Parcial
Single-stranded (+) 
Single-stranded (-) 
Single stranded, ambisense 
Double-stranded
Com proteínas ligadas covalentemente 
dsDNA com extremidades com ligação cruzada
DNA com RNA covalentemente ligado
�13
Os genomas de DNA ou RNA virais são 
estruturalmente diversos
AnAOH3’
UTR
5' VPg 
UTR
4252
3’
5’
A 
Linear (+) strand RNA genome of a picornavirus
B
�14
Genoma linear não quer 
dizer linha reta
Para que tanta diversidade?
• DNA e RNA
- Genomas de RNA apareceram primeiro na 
escala evolutiva (Mundo de RNA) - após 
resfriamento da Terra
- Surgimento dos genomas de DNA
- Os únicos genomas de RNA atualmente no 
planeta são virais
- Viróides: Relíquias do mundo de RNA?
�15
Influenza	virus
Reovirus
Hepatitis	B	virus
Parvovirus
Retrovirus
Poliovirus
©Principles of Virology, ASM Press
Genomas virais e exemplos
VII 
�16
Adenovirus
Herpes	simplex	virus
�17
Para quem tiver curiosidade
 
Taxonomy
Browse by Baltimore
Browse by host
Browse by virion
Data
Human viruses
Human Virus Size
Virosaurus
Vertebrate virus names
and acronyms
Reference sequences
Virus receptors
Virus molecular biology
Virion
Virus entry
Transcription,
replication, translation
Virus exit
Host-virus interactions
Virus genome evolution
Bacterial Viruses
Replication cycles
Focus
HIV resource
HBV resource
Herpesvirus resource
Links
e-Learning
About us
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Que informação é codificada pelo genoma viral?
Produtos e sinais para: 
- Replicação do genoma viral
- Processamento e empacotamento do 
genoma
- Controle e regulação do ciclo celular
- Modulação da defesa do hospedeiro
- Possibilidade de se espalhar para outras 
células e hospedeiros
�18
Informações que NÃO estão contidas em 
genomas virais
• Não há genes que codificam para todos os 
elementos da maquinaria síntese proteica (AARS, 
eIFs, tRNAs)
• Não há genes que codificam para o 
metabolismo energético ou biossíntese de 
membrana
• Não há centrômeros ou telômeros
• Será? Talvez ainda não tenhamos encontrado. 90% 
dos vírus gigantes são recém-descobertos
�19
Maiores genomas conhecidos
Virus Length Protein
Pandoravirus salinus 2,473,870 2,541
Pandoravirus dulcis 1,908,524 1,487
Megavirus chilensis 1,259,197 1,120
Mamavirus 1,191,693 1,023
Mimivirus 1,181,549 979
Moumouvirus 1,021,348 894
Mimivirus M4 981,813 620
C. roenbergensis virus 617,453 544
Mollivirus sibericum 651,000 523
Pithovirus sibericum 610,033 467
�20
Menores genomas conhecidos
Virus Length Protein
Viroid 120 none
Satellite 220 none
Hepatitis delta satellite 1,700 1
Circovirus 1,759 2
Anellovirus 2,170 4
Geminivirus 2,500 4
Hepatitis B virus 3,200 7
Levivirus 3,400 4
Partitivirus 3,700 2
Barnavirus 4,000 7
�21
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Nome da Sala: PERES2018 
Qual informação pode ser codificada por um genoma viral? 
a) Produtos que catalizam biossíntese de membrana. 
b) Produtos que catalizam produção de energia. 
c) Sistemas completos de síntese proteica. 
d) Centrômeros e telômeros. 
e) Enzimas para replicar o genoma viral. 
�22
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Genomas de DNA viral
• O genoma de todas as células hospedeiras é 
de DNA
• Entretanto o DNA viral não é como o de 
nossos cromossomos
�23
dsDNA
• Adenoviridae
• Herpesviridae
• Papillomaviridae
• Polyomaviridae
• Poxviridae
©Principles of Virology, ASM Press�24
dsDNA
Papillomaviridae (8 kbp)
Genomes copied by host DNA polymerase Genomes encode DNA polymerase
©Principles of Virology, ASM Press�25
dsDNA parcial
reverse 
transcriptaseRNAprotein
This genome cannot be copied to mRNA 
Hepadnaviridae 
Hepatitis B virus
©Principles of Virology, ASM Press�26
ssDNA
TT virus (ubiquitous human virus) B19 parvovirus(fifth disease)©Principles of Virology, ASM Press�27
SOCRATIVE
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Nome da Sala: PERES2018 
Qual dos genomas de DNA virais, ao entrar em uma célula, podem ser 
imediatamente transcritos? 
a) dsDNA. 
b) dsDNA parcial. 
c) ssDNA circular. 
d) ssDNA linear. 
e) Todos acima. 
�28
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Genomas de RNA
• Células não possuem RNA 
polimerases dependentes de RNA 
(RdRp)
• RNA virus codificam RdRp
• RdRp produz genomas de RNA e mRNA 
a partir de moldes de RNA
�29
Classificação de Baltimore
VII
©Principles of Virology, ASM Press�30
dsRNA
Rotavirus (human gastroenteritis)
©Principles of Virology, ASM Press�31
58 Chapter 3
However, RNA can be made only from a dsDNA template, 
whatever the sense of the ssDNA. Consequently, some DNA 
synthesis must precede mRNA production in the replication 
cycles of these viruses. Th e single-stranded viral genome is 
produced by cellular DNA polymerases. 
A dsRNA genome: Reoviridae B Reoviridae (19–32 kbp in 10 dsRNA segments)
 RNA
L1 L2 L3
M1 M2 M3
S1 S2 S4
 RNA
3'
5' c 3'
5'
3'
5'3'
5' c 3'
5'3'
5' c
3'
5'3'
5' c 3'
5'3'
5' c 3'
5'3'
5' c
S3
3'
5'3'
5' c
3'
5'3'
5' c
3'
5' c 3'
5' 3'
5' c 3'
5'
Figure 3.4 Structure and expression of viral double-stranded 
RNA genomes. (A) Synthesis of genomes, mRNA, and protein. 
(B) Genome configuration.
B A C K G R O U N D
RNA synthesis in cells
There are no known host cell enzymes that can copy the genomes of 
RNA viruses. However, at least one enzyme, RNA polymerase II, can 
copy an RNA template. The 1.7-kb circular, ssRNA genome of hepa-
titis delta satellite virus is copied by RNA polymerase II to form mul-
timeric RNAs (see the figure). How RNA polymerase II, an enzyme 
that produces pre-mRNAs from DNA templates, is reprogrammed to 
copy a circular RNA template is not known.
BOX 3.3
(–) strand
genome RNA
Hepatitis delta satellite (!) strand genome RNA is copied by 
RNA polymerase II at the indicated position. The polymerase pass-
es the poly(A) signal (purple box) and the self-cleavage domain (red 
circle). For more information, see Fig. 6.14. Redrawn from J. M. Taylor, 
Curr Top Microbiol Immunol 239:107–122, 1999, with permission.
 RNA Genomes 
 Cells have no RNA-dependent RNA polymerases that can 
replicate the genomes of RNA viruses or make mRNA from 
RNA templates (Box 3.3). One solution to this problem is 
that RNA virus genomes encode RNA-dependent RNA poly-
merases that produce RNA from RNA templates. The other 
solution, exemplified by retrovirus genomes, is reverse tran-
scription of the genome to dsDNA, which can be transcribed 
by host RNA polymerase. 
 dsRNA (Fig. 3.4) 
 Th ere are eight families of viruses with dsRNA genomes. 
Th e number of dsRNA segments ranges from 1 ( Totiviridae 
and Endornaviridae , viruses of fungi, protozoa, and plants) to 
9 to 12 ( Reoviridae , viruses of fungi, invertebrates, plants, pro-
tozoa, and vertebrates). While dsRNA contains a ( ! ) strand, 
it cannot be translated as part of a duplex to synthesize viral 
proteins. Th e ( " ) strand of the genomic dsRNA is fi rst cop-
ied into mRNAs by a viral RNA-dependent RNA polymerase. 
Newly synthesized mRNAs are encapsidated and then copied 
to produce dsRNAs. 
 ( ! ) Strand RNA (Fig. 3.5) 
 Th e ( ! ) strand RNA viruses are the most plentiful on this 
planet; 29 families have been recognized [not counting ( ! ) 
strand RNA viruses with DNA intermediates]. The fami-
lies Arteriviridae , Astroviridae , Caliciviridae , Coronaviridae , 
 Flaviviridae , Hepeviridae , Nodaviridae , Picornaviridae , and 
 Togaviridae include viruses that infect vertebrates. ( ! ) strand 
RNA genomes usually can be translated directly into protein 
by host ribosomes. Th e genome is replicated in two steps. Th e 
( ! ) strand genome is fi rst copied into a full-length ( " ) strand, 
and the ( " ) strand is then copied into full-length ( ! ) strand 
genomes. In some cases, a subgenomic mRNA is produced. 
ASM_POV4e_Vol1_Ch03.indd 58ASM_POV4e_Vol1_Ch03.indd 58 7/22/15 12:20 PM7/22/15 12:20 PM
• Picornaviridae (Poliovirus, Rhinovirus)
• Caliciviridae (gastroenteritis)
• Coronaviridae (SARS)
• Flaviviridae (Yellow fever virus, West Nile virus, Hepatitis C virus)
• Togaviridae (Rubella virus, Equine encephalitis virus)
ssRNA (+)
©Principles of Virology, ASM Press�32
ssRNA (+)
©Principles of Virology, ASM Press�33
58 Chapter 3
However, RNA can be made only from a dsDNA template, 
whatever the sense of the ssDNA. Consequently, some DNA 
synthesis must precede mRNA production in the replication 
cycles of these viruses. Th e single-stranded viral genome is 
produced by cellular DNA polymerases. 
A dsRNA genome: Reoviridae B Reoviridae (19–32 kbp in 10 dsRNA segments)
 RNA
L1 L2 L3
M1 M2 M3
S1 S2 S4
 RNA
3'
5' c 3'
5'
3'
5'3'
5' c 3'
5'3'
5' c
3'
5'3'
5' c 3'
5'3'
5' c 3'
5'3'
5' c
S3
3'
5'3'
5' c
3'
5'3'
5' c
3'
5' c 3'
5' 3'
5' c 3'
5'
Figure 3.4 Structure and expression of viral double-stranded 
RNA genomes. (A) Synthesis of genomes, mRNA, and protein. 
(B) Genome configuration.
B A C K G R O U N D
RNA synthesis in cells
There are no known host cell enzymes that can copy the genomes of 
RNA viruses. However, at least one enzyme, RNA polymerase II, can 
copy an RNA template. The 1.7-kb circular, ssRNA genome of hepa-
titis delta satellite virus is copied by RNA polymerase II to form mul-
timeric RNAs (see the figure). How RNA polymerase II, an enzyme 
that produces pre-mRNAs from DNA templates, is reprogrammed to 
copy a circular RNA template is not known.
BOX 3.3
(–) strand
genome RNA
Hepatitis delta satellite (!) strand genome RNA is copied by 
RNA polymerase II at the indicated position. The polymerase pass-
es the poly(A) signal (purple box) and the self-cleavage domain (red 
circle). For more information, see Fig. 6.14. Redrawn from J. M. Taylor, 
Curr Top Microbiol Immunol 239:107–122, 1999, with permission.
 RNA Genomes 
 Cells have no RNA-dependent RNA polymerases that can 
replicate the genomes of RNA viruses or make mRNA from 
RNA templates (Box 3.3). One solution to this problem is 
that RNA virus genomes encode RNA-dependent RNA poly-
merases that produce RNA from RNA templates. The other 
solution, exemplified by retrovirus genomes, is reverse tran-
scription of the genome to dsDNA, which can be transcribed 
by host RNA polymerase. 
 dsRNA (Fig. 3.4) 
 Th ere are eight families of viruses with dsRNA genomes. 
Th e number of dsRNA segments ranges from 1 ( Totiviridae 
and Endornaviridae , viruses of fungi, protozoa, and plants) to 
9 to 12 ( Reoviridae , viruses of fungi, invertebrates, plants, pro-
tozoa, and vertebrates). While dsRNA contains a ( ! ) strand, 
it cannot be translated as part of a duplex to synthesize viral 
proteins. Th e ( " ) strand of the genomic dsRNA is fi rst cop-
ied into mRNAs by a viral RNA-dependent RNA polymerase. 
Newly synthesized mRNAs are encapsidated and then copied 
to produce dsRNAs. 
 ( ! ) Strand RNA (Fig. 3.5) 
 Th e ( ! ) strand RNA viruses are the most plentiful on this 
planet; 29 families have been recognized [not counting ( ! ) 
strand RNA viruses with DNA intermediates]. The fami-
lies Arteriviridae , Astroviridae , Caliciviridae , Coronaviridae , 
 Flaviviridae , Hepeviridae , Nodaviridae , Picornaviridae , and 
 Togaviridae include viruses that infect vertebrates. ( ! ) strand 
RNA genomes usually can be translated directly into protein 
by host ribosomes. Th e genome is replicated in two steps. Th e 
( ! ) strand genome is fi rst copied into a full-length ( " ) strand, 
and the ( " ) strand is then copied into full-length ( ! ) strand 
genomes. In some cases, a subgenomic mRNA is produced. 
ASM_POV4e_Vol1_Ch03.indd 58ASM_POV4e_Vol1_Ch03.indd 58 7/22/15 12:20 PM7/22/15 12:20 PM
ssRNA(+) com intermediáriode DNA
Retroviridae 
Human immunodeficiency virus (HIV) 
Human T-lymphotropic virus (HTLV)
©Principles of Virology, ASM Press�34
Estratégia dos retrovírus
provirus
– DNA
+ RNA
+ RNA
DNA
©Principles of Virology, ASM Press�35
 Genomes and Genetics 59
turn are copied to produce ( ! ) strand genomes. Such RNA 
viral genomes can be either single molecules (nonsegmented; 
some viruses with this confi guration have been classifi ed in 
the order Mononegavirales ) or segmented. 
 The genomes of certain ( ! ) strand RNA viruses (e.g., 
members of the Arenaviridae and Bunyaviridae ) are ambi-
sense: they contain both ( " ) and ( ! ) strand information on a 
single strand of RNA (Fig. 3.7C). Th e ( " ) sense information 
in the genome is translated upon entry of the viral RNA into 
cells. Replication of the RNA genome yields additional ( " ) 
sense information, which is then translated. 
 What Do Viral Genomes Look Like? 
 Some small RNA and DNA genomes enter cells from virus 
particles as naked molecules of nucleic acid, whereas others 
are always associated with specialized nucleic acid-binding 
proteins. A fundamental difference between the genomes of 
viruses and those of hosts is that although viral genomes are 
often covered with proteins, they are usually not bound by 
histones (polyomaviral and papillomaviral genomes are an 
exception). 
 ( " ) Strand RNA with DNA Intermediate (Fig. 3.6) 
 In contrast to other ( " ) strand RNA viruses, the ( " ) strand 
RNA genome of retroviruses is converted to a dsDNA inter-
mediate by viral RNA-dependent DNA polymerase (reverse 
transcriptase). Th is DNA then serves as the template for viral 
mRNA and genome RNA synthesis by cellular enzymes. Th ere 
are three families of ( " ) strand RNA viruses with a DNA 
intermediate; members of the Retroviridae infect vertebrates. 
 ( ! ) Strand RNA (Fig. 3.7) 
 Viruses with ( ! ) strand RNA genomes are found in 
seven families. Viruses of this type that can infect vertebrates 
include members of the Bornaviridae , Filoviridae , Ortho-
myxoviridae , Paramyxoviridae , and Rhabdoviridae families. 
Unlike ( " ) strand RNA, ( ! ) strand RNA genomes cannot 
be translated directly into protein, but must be fi rst copied to 
make ( " ) strand mRNA. Th ere are no enzymes in the cell that 
can make mRNAs from the RNA genomes of ( ! ) strand RNA 
viruses. Th ese virus particles therefore contain virus-encoded 
RNA-dependent RNA polymerases. Th e genome is also the 
template for the synthesis of full-length ( " ) strands, which in 
A ss (+) RNA: Coronaviridae, Flaviviridae, Picornaviridae,
 Togaviridae
B Coronaviridae (28–33 kb)
UTR
– RNA
Genome
AnAOH3’'
UTR
5' c
UTR
B Flaviviridae (10–12 kb)
5' c 3'
B Picornaviridae (7–8.5 kb)
UTR
B Togaviridae (10–13 kb)
5' c
UTR
5' VPg
UTR
UTR
AnAOH3’'
UTR
AnAOH3’
Figure 3.5 Structure and expression of viral single-stranded 
(!) RNA genomes. (A) Synthesis of genomes, mRNA, and protein. (B) 
Genome configurations. UTR, untranslated region. 
A ss (+) RNA with DNA intermediate: Retroviridae
B Retroviridae (7–10 kb)
– DNA
+ RNA
+ RNA
AnAOH3’
 DNA
5' c
U5 U3
Figure 3.6 Structure and expression of viral single-stranded 
(!) RNA genomes with a DNA intermediate. (A) Synthesis of 
genomes, mRNA, and protein. (B) Genome configuration. 
ASM_POV4e_Vol1_Ch03.indd 59ASM_POV4e_Vol1_Ch03.indd 59 7/22/15 12:20 PM7/22/15 12:20 PM
ssRNA (-)
•Paramyxoviridae (vírus da rubéola, vírus da 
caxumba) 
•Rhabdoviridae (vírus da raiva) 
•Filoviridae (vírus Ebola, vírus de Marburg) 
•Orthomyxoviridae (vírus Influenza)
©Principles of Virology, ASM Press�36
ssRNA (-)
– RNA
– RNA+ RNA
©Principles of Virology, ASM Press�37
 Genomes and Genetics 59
turn are copied to produce ( ! ) strand genomes. Such RNA 
viral genomes can be either single molecules (nonsegmented; 
some viruses with this confi guration have been classifi ed in 
the order Mononegavirales ) or segmented. 
 The genomes of certain ( ! ) strand RNA viruses (e.g., 
members of the Arenaviridae and Bunyaviridae ) are ambi-
sense: they contain both ( " ) and ( ! ) strand information on a 
single strand of RNA (Fig. 3.7C). Th e ( " ) sense information 
in the genome is translated upon entry of the viral RNA into 
cells. Replication of the RNA genome yields additional ( " ) 
sense information, which is then translated. 
 What Do Viral Genomes Look Like? 
 Some small RNA and DNA genomes enter cells from virus 
particles as naked molecules of nucleic acid, whereas others 
are always associated with specialized nucleic acid-binding 
proteins. A fundamental difference between the genomes of 
viruses and those of hosts is that although viral genomes are 
often covered with proteins, they are usually not bound by 
histones (polyomaviral and papillomaviral genomes are an 
exception). 
 ( " ) Strand RNA with DNA Intermediate (Fig. 3.6) 
 In contrast to other ( " ) strand RNA viruses, the ( " ) strand 
RNA genome of retroviruses is converted to a dsDNA inter-
mediate by viral RNA-dependent DNA polymerase (reverse 
transcriptase). Th is DNA then serves as the template for viral 
mRNA and genome RNA synthesis by cellular enzymes. Th ere 
are three families of ( " ) strand RNA viruses with a DNA 
intermediate; members of the Retroviridae infect vertebrates. 
 ( ! ) Strand RNA (Fig. 3.7) 
 Viruses with ( ! ) strand RNA genomes are found in 
seven families. Viruses of this type that can infect vertebrates 
include members of the Bornaviridae , Filoviridae , Ortho-
myxoviridae , Paramyxoviridae , and Rhabdoviridae families. 
Unlike ( " ) strand RNA, ( ! ) strand RNA genomes cannot 
be translated directly into protein, but must be fi rst copied to 
make ( " ) strand mRNA. Th ere are no enzymes in the cell that 
can make mRNAs from the RNA genomes of ( ! ) strand RNA 
viruses. Th ese virus particles therefore contain virus-encoded 
RNA-dependent RNA polymerases. Th e genome is also the 
template for the synthesis of full-length ( " ) strands, which in 
A ss (+) RNA: Coronaviridae, Flaviviridae, Picornaviridae,
 Togaviridae
B Coronaviridae (28–33 kb)
UTR
– RNA
Genome
AnAOH3’'
UTR
5' c
UTR
B Flaviviridae (10–12 kb)
5' c 3'
B Picornaviridae (7–8.5 kb)
UTR
B Togaviridae (10–13 kb)
5' c
UTR
5' VPg
UTR
UTR
AnAOH3’'
UTR
AnAOH3’
Figure 3.5 Structure and expression of viral single-stranded 
(!) RNA genomes. (A) Synthesis of genomes, mRNA, and protein. (B) 
Genome configurations. UTR, untranslated region. 
A ss (+) RNA with DNA intermediate: Retroviridae
B Retroviridae (7–10 kb)
– DNA
+ RNA
+ RNA
AnAOH3’
 DNA
5' c
U5 U3
Figure 3.6 Structure and expression of viral single-stranded 
(!) RNA genomes with a DNA intermediate. (A) Synthesis of 
genomes, mRNA, and protein. (B) Genome configuration. 
ASM_POV4e_Vol1_Ch03.indd 59ASM_POV4e_Vol1_Ch03.indd 59 7/22/15 12:20 PM7/22/15 12:20 PM
L R3M
©Principles of Virology, ASM Press�38
A consequência do genoma segmentado
Genomas RNA ambisense
Arenaviridae 
RNA pol in virion
©Principles of Virology, ASM Press�39
SOCRATIVE
Acessar: https://b.socrative.com/login/student/ 
(Ou baixar o aplicativo Socrative Student em seu celular) 
Nome da Sala: PERES2018 
Qual afirmação é correta acerca dos genomas virais de RNA? 
a) Genomas ss(+)RNA podem ser traduzidos para formação de proteínas virais. 
b) Genomas de dsRNA podem ser imediatamente traduzidos ao infectar uma 
célula. 
c) Vírus ss(+)RNA não requerem a formação de um intermediário RNA (-). 
d) Genomas virais de RNA podem ser copiados por RNA polimerases do 
hospedeiro. 
e) Todas acima. 
�40
Interatividade
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Importantes definições
❖uma célula suscetível tem um receptor 
para determinado vírus – a célula pode ou 
não dar suporte à replicação viral 
❖uma célula resistente não tem receptor –
pode ou não ser competente à replicação 
viral 
❖uma célula permissível tem a capacidade 
dereplicar o vírus – a célula pode ou não 
ser suscetível 
❖uma célula suscetível e permissível é a única 
célula capaz de ser infectada e dar condições 
para sua replicação
Funções celulares
Estudo do ciclo infeccioso dos vírus nas células
✓ Só foi possível após 
1949 
✓ Enders, Weller e 
Robbins propagaram 
Poliovirus em cultura 
de células humanas 
✓ Prêmio Nobel - 1954
Cultivo de vírus
Fibroblastos humanos Fibroblastos de rato Célula epitelial 
humana (HeLa)
Linhagens 
imortalizadas
 The Infectious Cycle 33
 Th ere are three main kinds of cell cultures (Fig. 2.7), each 
with advantages and disadvantages. Primary cell cultures are 
prepared from animal tissues as described above. Th ey have a 
limited life span, usually no more than 5 to 20 cell divisions. 
Commonly used primary cell cultures are derived from mon-
key kidneys, human embryonic amnion and kidneys, human 
foreskins and respiratory epithelium, and chicken or mouse 
embryos. Such cells are used for experimental virology 
when the state of cell diff erentiation is important or when 
appropriate cell lines are not available. Th ey are also used 
in vaccine production: for example, live attenuated poliovi-
rus vaccine strains may be propagated in primary monkey 
kidney cells. Primary cell cultures were mandated for the 
growth of viruses to be used as human vaccines to avoid con-
tamination of the product with potentially oncogenic DNA 
from continuous cell lines (see below). Some viral vaccines 
are now prepared in diploid cell strains , which consist of a 
homogeneous population of a single type and can divide up 
to 100 times before dying. Despite the numerous divisions, 
these cell strains retain the diploid chromosome number. 
The most widely used diploid cells are those established 
from human embryos, such as the WI-38 strain derived from 
human embryonic lung. 
 Continuous cell lines consist of a single cell type that can 
be propagated indefi nitely in culture. Th ese immortal lines 
are usually derived from tumor tissue or by treating a pri-
mary cell culture or a diploid strain with a mutagenic chem-
ical or a tumor virus. Such cell lines oft en do not resemble 
the cell of origin; they are less diff erentiated (having lost the 
morphology and biochemical features that they possessed in 
the organ), are oft en abnormal in chromosome morphology 
and number ( aneuploid ), and can be tumorigenic (i.e., they 
produce tumors when inoculated into immunodeficient 
mice). Examples of commonly used continuous cell lines 
include those derived from human carcinomas (e.g., HeLa 
[Henrietta Lacks] cells; Box 2.3) and from mice (e.g., L and 
3T3 cells). Continuous cell lines provide a uniform popula-
tion of cells that can be infected synchronously for growth 
Figure 2.7 Different types of cell culture used in virology. Confluent cell monolayers photographed by 
low-power light microscopy. (A) Primary human foreskin fibroblasts; (B) established line of mouse fibroblasts (3T3); 
(C) continuous line of human epithelial cells (HeLa [Box 2.3]). The ability of transformed HeLa cells to overgrow one 
another is the result of a loss of contact inhibition. Courtesy of R. Gonzalez, Princeton University.
curve analysis (see “Th e One-Step Growth Cycle” below) or 
biochemical studies of virus replication. 
 In contrast to cells that grow in monolayers on plastic 
dishes, others can be maintained in suspension cultures , in 
which a spinning magnet continuously stirs the cells. The 
advantage of suspension culture is that a large number of 
cells can be grown in a relatively small volume. Th is culture 
method is well suited for applications that require large quan-
tities of virus particles, such as X-ray crystallography or pro-
duction of vectors. 
 Because viruses are obligatory intracellular parasites, they 
cannot reproduce outside a living cell. An exception comes 
from the demonstration in 1991 that infectious poliovirus 
could be produced in an extract of human cells incubated 
with viral RNA. Similar extracellular replication of the com-
plete viral infectious cycle has not been achieved for any other 
virus. Consequently, most analysis of viral replication is done 
using cultured cells, embryonated eggs, or laboratory animals 
(Box 2.4). 
 Evidence of Viral Growth in Cultured Cells 
 Some viruses kill the cells in which they reproduce, and 
the infected cells may eventually detach from the cell cul-
ture plate. As more cells are infected, the changes become 
visible and are called cytopathic eff ects (Table 2.1). Many 
types of cytopathic eff ect can be seen with a simple light or 
phase-contrast microscope at low power, without fi xing or 
staining the cells. Th ese changes include the rounding up and 
detachment of cells from the culture dish, cell lysis, swelling 
of nuclei, and sometimes the formation of a group of fused 
cells called a syncytium (Fig. 2.8). Observation of other 
cytopathic effects requires high-power microscopy. These 
cytopathic eff ects include the development of intracellular 
masses of virus particles or unassembled viral components in 
the nucleus and/or cytoplasm (inclusion bodies), formation of 
crystalline arrays of viral proteins, membrane blebbing, dupli-
cation of membranes, and fragmentation of organelles. Th e 
time required for the development of cytopathology varies 
ASM_POV4e_Vol1_Ch02.indd 33ASM_POV4e_Vol1_Ch02.indd 33 7/22/15 12:13 PM7/22/15 12:13 PM
<shorturl.at/mFYZ6>
http://shorturl.at/mFYZ6
Os vírus superaram o dogma de um 
gene para uma proteína
• Vírus podem ter uma expressão 
gênica muito resumida 
• Vírus podem fazer múltiplas proteínas 
a partir de um gene: 
• Fazendo grandes poliproteínas e clivando-as em 
várias proteínas menores 
• Possuindo “overlapping reading frames” 
(diferentes fases de leitura) 
• Utilizando múltiplos sítios para começar a 
tradução
<shorturl.at/sBMQY>
�45
http://shorturl.at/sBMQY
• Influenza virus - 1933
• Em 2005, o RNA do vírus Influenza (H1N1 - gripe espanhola de 1918) foi isolado de 
tecidos emblocados em parafina, provenientes de uma autópsia realizada em 1918
• O RNA viral também foi isolado a partir de biópsias de cadáveres enterrados no 
permafrost desde 1918 
• O sequenciamento completo indicou a presença de 8 segmentos diferentes de RNA
• O vírus pôde ser reconstruído ao se transfectar células com 8 plasmídeos recombinantes 
distintos, cada um contendo uma das sequências do genoma viral
�46
©Principles of Virology, ASM Press�47
Virologia sintética e biossegurança
<shorturl.at/jrsJR><shorturl.at/fnyP0>
http://shorturl.at/jrsJR
http://shorturl.at/fnyP0
Legal, não?
�48
Obrigado pela atenção!