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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 -> DNA
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 proteins
(+ve) sense mRNA AAA
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Need to make mRNA MINUS (NEGATIVE) SENSE RNA GENOMES proteins
(+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. proteins (+ve) sense mRNA AAA If used, RNA modifying enzymes are packaged in virion. (-ve) sense genomic RNA
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Need to make mRNA DOUBLE-STRANDED RNA GENOMES RNA polymerase must be
packaged in virion. proteins (+ve) sense mRNA AAA If used, RNA modifying enzymes are packaged in virion. 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
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RETROVIRUSES Genome RNA-dependent DNA polymerase
(=reverse transcriptase) in virion Infectivity of RNA Initial event in cell Plus-stranded RNA Yes Non-infectious Reverse transcription
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GENOME SIZE 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
AAAAAAAA RIBOSOMES mRNA PROTEIN 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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