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Structural Virology
Lecture 3
Pavel Plevka
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T = h2 + hk + k2
Quasi equivalence
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Transcription, Translation, and Transport
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Transcription, Translation, and Transport
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(David) Baltimore virus
classification
- genome type
- mode of transcription
- (-) and (+) relative to mRNA
- ambisense viruses (ssDNA geminiviruses,
arenaviruses)
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Central Dogma of Molecular Biology
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Transcription in Eukaryotes
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Promoters, Enhancers, and TATA box
T A T A A/T A A/T A/G
General cellular transcription factors: TFIID
Specific cellular transcription factors.
Virus transcription factors: VP16 of herpes simplex virus
- different transcription factors used during different stages of infection
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Transcriptases
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mRNA cap
Guanosine triphosphate
joined by 5’-5’ linkage
(methylated in ribose)
• aid mRNA transport from the
nucleus to the cytoplasm
• protect the mRNA from
degradation by exonucleases
• required for the initiation of
translation
RNA triphosphatase
Guanylyl transferase
Methyl transferase(s)
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Cell enzymes:
• RNA triphosphatase
• Guanylyl transferase
• Methyl transferase(s)
Influenza virus – cap snatching
Poxviruses, coronaviruses, reoviruses replicate in cytoplasm
and encode own capping enzymes.
Cap snatching in cytoplasm – bunyaviruses
Non-capped mRNAs – picornaviruses
De-capping of host mRNAs – totiviruses
Obtaining mRNA cap
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mRNA polyadenylation
A A T A A A
Poly(a) polymerase
First identified in SV40 transcripts in 1981.
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Pre-mRNA splicing
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Translation
• Most viruses use host
translation machinery.
• Mimiviruses encode their own
tRNAs.
• eukaryotic Initiation Factors
(eIF) (CAP)
• polyA binding proteins
• mRNA circularization
• 5’->3’ scanning by 40S subunit
(AUG) x Sendai virus (ACG)
• IRES
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IRES dependent Translation
Hepatitis C virus
Picornaviruses
Kaposi’s sarcoma associated herpesvirus
Some cellular mRNAs
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Bicistronic mRNAs
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Bicistronic mRNAs of dicistroviruses
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Co- and post translational protein modification
N-glycosylation
(Asn)
O-glycosylation
(Tyr, Ser)
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Co- and post translational protein modification
Acylation (addition of Myristic acid)
- Gag of HIV
- VP4 of picornaviruses
Phosphorylation
- serine, threonine, tyrosine
Cleavage
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Targeting of virus proteins
Nuclear localization signal:
PKKKRKV
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Transcription in bacteria
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• explain how virus genes are transcribed and
translated
• describe the post-translational modifications
that some virus proteins undergo
• highlight differences in transcription and
transla- tion between prokaryotic and
eukaryotic cells
• discuss the transport of virus proteins and
RNA within cells
Learning outcomes
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Virus Genome Replication
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Priming of NA synthesis
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Location of virus replication sites in eucaryotes
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Leading and Lagging strands in
dsDNA replication
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Rolling circle x “normal” replication
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Conservative x semiconservative replication
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Replication of retroviruses
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• state the locations within eukaryotic cells
where different categories of virus genome
are replicated
• explain the role of primers in virus nucleic
acid synthesis
• discuss the roles of virus and host proteins in
virus genome replication
• outline the replication mechanisms of virus
DNAs and RNAs
• explain the term ‘reverse transcription’
Learning outcomes