Lecture 3 - He

Question 1

What is the primary block for the Y mutant virus cell line B that only expresses the mRNA of alpha genes?

Answer 1

• translation is being blocked.
• a genes: mRNA is already present, but protein synthesis is inhibited
• b, y genes: no transcription of mRNA

Question 2

in cell line B, what is the status of EIF2a after infection with the Y mutant virus”?

Answer 2

• EIF2a is phosphorylated, and therefore protein synthesis is inhibited. Translation does not occur

Question 3

wt HSV is able to infect cell line B unline Y mutant virus. List a possible mechanism by which Y gene product might work.

Answer 3

The Y gene may inhibit PKR. Inhibiting PKR leads to the activation of EIF2a so that protein synthesis may occur.

So without the Y gene, PKR prevents protein synthesis from occuring.

• Could also inhibit the upregulation of PKR that occurs via IFN.

Question 4

Ras

Answer 4

Ras BLOCKS PKR = EIF2a on = protein synth

Question 5

Master switch and viral genes

Answer 5

VP16 = master switch
a genes = mRNA is already present but needs to be translated
b genes: de novo, need to be transcribed. Expression initiates DNA replication
y genes: viral DNA synthesis. Contains packaging so that virus can propagate to other cells.

Question 6

mutation that leads to non-pathogenic virus

Answer 6

y34.5,
virus cant overcome the restriction by PKR.

y34.5 normally hijacks host protein PP1 and forms a complex to reactivate EIF2a.