rna virus replication strategies
DESCRIPTION
RNA VIRUS REPLICATION STRATEGIES. 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 . RNA -> RNA. RNA-dependent RNA polymerase . RNA -> DNA. - PowerPoint PPT PresentationTRANSCRIPT
1
46 54 60 64 68 71 75 820
1
2
3
4
5
6
7
8
Frequency
Frequency
2
RNA VIRUS REPLICATION STRATEGIES
3
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
4
5
6
7
RNA VIRUS STRATEGIES
RNA -> RNARNA-dependent RNA polymerase
RNA -> DNARNA-dependent DNA polymerase- reverse transcriptase
Host cell DNA -> RNADNA-dependent RNA polymerase
8
ALL ANIMAL RNA VIRUSES CODE FOR A POLYMERASE
9
Need to make mRNA
PLUS (POSITIVE) SENSE RNA GENOMES
AAA(+ve) sense mRNA
10
Need to make mRNA
MINUS (NEGATIVE) SENSE RNA GENOMES
AAA(+ve) sense mRNA
(-ve) sense genomic RNA
11
Need to make mRNA
MINUS (NEGATIVE) SENSE RNA GENOMES
RNA polymerase must bepackaged in virion.
AAA(+ve) sense mRNA
(-ve) sense genomic RNAIf used, RNA modifying enzymes arepackaged in virion.
12
Need to make mRNA
DOUBLE-STRANDED RNA GENOMES
AAA(+ve) sense mRNA
Double-stranded genomic RNAIf used, RNA modifying enzymes arepackaged in virion.
RNA polymerase must bepackaged in virion.
13
Need to make mRNA
RETROVIRUSES
DSDNA
+VE RNA
DSDNA
Reverse transcriptase mustbe packaged in virion.
14
RNA viruses that do NOT have a DNA phase
TranscriptionNon-infectiousYesDouble-stranded RNA
TranscriptionNon-infectiousYesNegative-stranded RNA
TranslationInfectiousNoPlus-stranded RNA
Initial event in cell
Infectivity of RNA
RNA-dependent RNA polymerase (=transcriptase) IN VIRION
Genome
TranscriptionNon-infectiousYesDouble-stranded RNA
TranscriptionNon-infectiousYesNegative-stranded RNA
TranslationInfectiousNoPlus-stranded RNA
Initial event in cell
Infectivity of RNA
RNA-dependent RNA polymerase (=transcriptase) IN VIRION
Genome
15
Genome RNA-dependent DNA polymerase (=reverse transcriptase) in virion
Infectivity of RNA
Initial event in cell
Plus-stranded RNA Yes Non-infectious Reverse
transcription
RETROVIRUSES
16
17
GENOME SIZE
• POLYMERASE• ATTACHMENT PROTEIN• CAPSID PROTEIN• RELATIVELY FEW OTHER PROTEINS• VIRION SIZE MAY BE QUITE LARGE
BUT LIMITED NUMBER OF PROTEINS
18
The monocistronic mRNA problem
• 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
AAAAAAAA
RIBOSOMES
mRNA
PROTEIN
AAAAAAAA
19
20
21
22
23
24
GENOME SIZE
• TAUTOMERIZATION• PROOF READING