lecture 6

Question 1

what polymerase does replication use?

Answer 1

DNa dependent DNA polymerase, templates DNA

Question 2

what polymerase does transcription use?

Answer 2

DNA dependent RNA polymerase, template DNA

Question 3

what polymerase does retrovirus use?

Answer 3

RNA dependent DNA polymerase aka reverse transcriptase

Question 4

what polymerase does RNA virus replication use?

Answer 4

RNA dependent RNA polymerase

Question 5

Where does RNA polymerase bind on a genome?

Answer 5

TATAA box

Question 6

What elements aid in polymerase binding

Answer 6

transcription factors and enhancers (about 100-200bp upstream)

Question 7

what is the 7mG cap?

Answer 7

7 methylguanylate cao structure at the 5’end of an mRNA
- recognized by ribosome to initiate translation

Question 8

What is a polyadynlation tail?

Answer 8

long string of A bases that protect the mRNA from degradation

Question 9

what happens with (-) strand rhabdoviral poly A tailed mRNA?

Answer 9

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

Question 10

What does guanyltransferase do?

Answer 10

add a guanine base at the 5’ end of a transcript, then a methyltransferase adds a methyl group

Question 11

how do caps work?

Answer 11

ribosome binds 7 mG cap on mRNA, moves down looking for good start codon, falls off at stop site

Question 12

What are the two cap like structures?

Answer 12

VPG and IRES(no cap necessary)

Question 13

what is a vpg?

Answer 13

viral protein genome linked, covalently linked to the 5’ end and recognized by the ribosome, translation initiated

Question 14

What is IRES?

Answer 14

no cap necessary, RNA sequences that can bind to the ribosome and initiate translation in two different sites

Question 15

what does cap snatching achieve

Answer 15

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

Question 16

What is IRES mediated translation?

Answer 16

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

Question 17

What is transcriptional control of viral gene expression

Answer 17

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

Question 18

WAVES: immediate early genes

Answer 18

regulatory genes, does not require viral protein synthesis, immediately transcribed upon entry, turn on early gene expression

Question 19

WAVES 2: early genes

Answer 19

requires the product of immediate early genes
- polymerase, helices, ssb
doesn’t use host polymerase
replicate genome via rolling circle replication

Question 20

WAVES 3: structural genes

Answer 20

full expression requires replication of genome
capsid proteins, glycoproteins, assembly proteins

Question 21

differential transcription, - strand

Answer 21

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

Question 22

What are some mechanisms by which viruses overcome one gene one protein?

Answer 22

compact gene expression
-polyprotein processing
- overlapping reading frames
-utilizing multiple start sites
- multiple splice variants