lecture 6 Flashcards
what polymerase does replication use?
DNa dependent DNA polymerase, templates DNA
what polymerase does transcription use?
DNA dependent RNA polymerase, template DNA
what polymerase does retrovirus use?
RNA dependent DNA polymerase aka reverse transcriptase
what polymerase does RNA virus replication use?
RNA dependent RNA polymerase
Where does RNA polymerase bind on a genome?
TATAA box
What elements aid in polymerase binding
transcription factors and enhancers (about 100-200bp upstream)
what is the 7mG cap?
7 methylguanylate cao structure at the 5’end of an mRNA
- recognized by ribosome to initiate translation
What is a polyadynlation tail?
long string of A bases that protect the mRNA from degradation
what happens with (-) strand rhabdoviral poly A tailed mRNA?
makes 7 mRNAS from - strand
- one polymerase slides across the whole genome and releases each mRA
- U string in intergenic region causes polymerase slipping and adding hundreds of A bases
What does guanyltransferase do?
add a guanine base at the 5’ end of a transcript, then a methyltransferase adds a methyl group
how do caps work?
ribosome binds 7 mG cap on mRNA, moves down looking for good start codon, falls off at stop site
What are the two cap like structures?
VPG and IRES(no cap necessary)
what is a vpg?
viral protein genome linked, covalently linked to the 5’ end and recognized by the ribosome, translation initiated
What is IRES?
no cap necessary, RNA sequences that can bind to the ribosome and initiate translation in two different sites
what does cap snatching achieve
eliminates ned=ed for virus to encode cap enzymes
cap makes immune evasion possible, viral mRNA is no longer viewed as foreign
- viral mRNA translation is activated, while host is deactivated, kill off host
What is IRES mediated translation?
RNA virus have RNA structure upstream of start codon, structure binds to ribosome, ribosome think its a cap
In DNA virus, allows one mRNA to make 2 proteins
What is transcriptional control of viral gene expression
proteins expressed at optimal time, at optimal quality
(+) strand: one mRNA usually so temporal control via cleavage of large poly protein
(-) strand: can make more mRNA and control level made
WAVES: immediate early genes
regulatory genes, does not require viral protein synthesis, immediately transcribed upon entry, turn on early gene expression
WAVES 2: early genes
requires the product of immediate early genes
- polymerase, helices, ssb
doesn’t use host polymerase
replicate genome via rolling circle replication
WAVES 3: structural genes
full expression requires replication of genome
capsid proteins, glycoproteins, assembly proteins
differential transcription, - strand
HSV polymerase runs down genome and makes polyA mRNA but does not fall off
makes 5 mRNA but may fall off before making different levels of each
What are some mechanisms by which viruses overcome one gene one protein?
compact gene expression
-polyprotein processing
- overlapping reading frames
-utilizing multiple start sites
- multiple splice variants
