RNA Virus Replication

Question 1

General comments

Answer 1

*Replicate in the cytoplasm of the cell except for orthomyxoviruses (e.g., influenza virus and retroviruses [e.g., HIV])
*Single-stranded (s.s.) RNA viruses have either a positive (+) sense (messenger polarity), negative (-) sense (antimessenger polarity), or ambisence polarity (both + and -)
*All negative-sense RNA viruses are enveloped
*Since cells lack cytoplasmic RNA polymerase, RNA viruses must produce their own replicase/transcriptase

Question 2

RNA Virus Genome Replication

Answer 2

Negative sense RNA viruses have a replicase/transcriptase associated with the RNA within the virion
All s.s. RNA viruses except retroviruses replicate via a double-stranded RNA intermediate
Retroviruses have a nuclear phase, involving a reverse transcriptase in their genomic RNA replication
The spontaneous mutation frequency of RNA viruses is higher than the DNA viruses because their RNA polymerase are not as accurate in duplication

Question 3

Expression of RNA Genomes

Answer 3

Transcription of orthomyxoviruses and retrovirus mRNA occurs in the nucleus
RNA viruses have developed unique mechanisms to produce individual polypeptides from polycistronic RNA since this is not a property of eukaryotic cells
– picornavirus synthesize polypeptides that are then cleaved by viral proteases
– individual initiation and termination signals appear throughout RNA of rabies virus

Each virus family has unique way of making necessary proteins. HIV synthesizes a long polypeptide and has a protease that cuts it for diff functions. This protease is key drug target.

Question 4

expression of RNA Genomes, ctd.

Answer 4

All transcription begins on 3’ end, but polymerase slides over various size intervening sequences to yield transcript of various compositions and lengths
– Orthomyxoviruses and reoviruses have segmented genomes
– retroviruses have spliced transcripts
Some RNA viruses use a combination of strategies

Viruses that have segmented genome, each segment codes for single or maybe two polypeptides.

Question 5

RNA Virus Table

Answer 5

Differ in all sorts of ways. …genome size,replication site, enveloped or not, morphology (shape) +/- sense.

- sense guys use replicase/transcriptase to make + sense to make mRNA to translate protein