Download rna virus replication strategies

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RNA VIRUS REPLICATION
STRATEGIES
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Objectives
• Classes of RNA genomes Baltimore
Classification
• Different strategies used by RNA
viruses
• RNA replication and mRNA synthesis
• Initiation, elongation and termination of
replication
• Examples
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RNA VIRUS STRATEGIES
RNA -> RNA
RNA-dependent RNA polymerase
RNA -> DNA
RNA-dependent DNA polymerase
- reverse transcriptase
Host cell DNA -> RNA
DNA-dependent RNA polymerase
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ALL ANIMAL RNA VIRUSES
CODE FOR A POLYMERASE
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Need to make mRNA
PLUS (POSITIVE) SENSE RNA GENOMES
(+ve) sense mRNA
AAA
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Need to make mRNA
MINUS (NEGATIVE) SENSE RNA GENOMES
(+ve) sense mRNA
AAA
(-ve) sense genomic RNA
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Need to make mRNA
MINUS (NEGATIVE) SENSE RNA GENOMES
RNA polymerase must be
packaged in virion.
(+ve) sense mRNA
If used, RNA modifying
enzymes are
packaged in virion.
AAA
(-ve) sense genomic RNA
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Need to make mRNA
DOUBLE-STRANDED RNA GENOMES
RNA polymerase must be
packaged in virion.
(+ve) sense mRNA
If used, RNA modifying
enzymes are
packaged in virion.
AAA
Double-stranded genomic RNA
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Need to make mRNA
RETROVIRUSES
Reverse transcriptase must
be packaged in virion.
DS
DNA
DS
DNA
+VE
RNA
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RNA viruses that do NOT have a DNA
phase
Genome
RNA-dependent Infectivity of
RNA
RNA
polymerase
(=transcriptase)
IN VIRION
Initial event in
cell
Plus-stranded
RNA
No
Infectious
Translation
Negativestranded RNA
Yes
Non-infectious Transcription
Doublestranded RNA
Yes
Non-infectious Transcription
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RETROVIRUSES
Genome
Plus-stranded
RNA
RNAdependent
DNA
polymerase
(=reverse
transcriptase)
in virion
Infectivity of
RNA
Initial event in
cell
Yes
Non-infectious
Reverse
transcription
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GENOME SIZE
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POLYMERASE
ATTACHMENT PROTEIN
CAPSID PROTEIN
RELATIVELY FEW OTHER PROTEINS
VIRION SIZE MAY BE QUITE LARGE
BUT LIMITED NUMBER OF
PROTEINS
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The monocistronic mRNA problem
mRNA
AAAAAAAA
RIBOSOMES
PROTEIN
AAAAAAAA
• Make one monocistronic mRNA per protein
• Make a primary transcript and use alternative splicing
• Make a large protein and then cut it into smaller
proteins
• Include special features in the mRNA which enable
ribosomes to bind internally
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GENOME SIZE
• TAUTOMERIZATION
• PROOF READING
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