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

7. 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

8. ALL ANIMAL RNA VIRUSES CODE FOR A POLYMERASE

9. Need to make mRNA PLUS (POSITIVE) SENSE RNA GENOMES proteins
(+ve) sense mRNA
AAA

10. Need to make mRNA MINUS (NEGATIVE) SENSE RNA GENOMES proteins
(+ve) sense mRNA
AAA
(-ve) sense genomic RNA

11. 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

12. 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

13. Need to make mRNA RETROVIRUSES Reverse transcriptase must
be packaged in virion. DS
DNA DS
DNA
+VE
RNA

14. RNA viruses that do NOT have a DNA phase

15. 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

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
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

24. GENOME SIZE
TAUTOMERIZATION
PROOF READING