Lecture 14 - Herpes 4

Question 1

What 2 features of viral mRNA resemble the host and allow it to be spliced by host enzymes?

Answer 1

5’ caps and poly A tail

Question 2

What are the 3 canonical rules herpes virus genomes must obey to be expressed?

Answer 2

1) mRNA splicing in nucleus
2) export to cytoplasm
3) translation initiation, elongation and termination

Question 3

What are the 2 functions of Herpesviruses mRNA processing proteins?

Answer 3

1) aid export of unspliced viral mRNA

2) inhibit export of host mRNA

Question 4

Viral mRNA is considered to be unspliced if contains ___ or lacks ___ ___

Answer 4

Viral mRNA is considered to be unspliced if it contains introns or lacks splice junctions

Question 5

What are the 2 requirements for initiation of herpesviral translation to occur?

Answer 5

1) ternary complex formation

2) cap-binding complex

Question 6

What is the function of the cap binding complex? What is the name of the major protein involved?

Answer 6

Capped ends of the viral mRNA are brought together with proteins to circularize the genome. eIF4F is the major protein involved

Question 7

What are the 2 regulatory points of translation initiation? How are they regulated?

Answer 7

Cap-binding complex formation and ternary complex formation. They are regulated by phosphorylation cascades

Question 8

What is the function of the ternary complex? What are the molecules involved?

Answer 8

The ternary complex is formed with the small ribosomal subunit and then binds to viral mRNA. The complex scans for a start codon. Upon locating a start codon, the large ribosomal subunit binds and translation is initiated.

Question 9

What protein regulates ternary complex formation?

Answer 9

elF2a

• Phosphorylation of elF2a blocks ternary complex formation and therefore translation initiation
• Dephosphorylation of elF2a allows ternary complex formation and initiates translation initiation

Question 10

How is elF2a prevented from allowing ternary complex formation?

Answer 10

Phosphorlyation by cellular PKR

Question 11

Describe the role of PKR in translational initiation regulation

Answer 11

PKR is a kinase that phosphorylates (deactivates) elF2a upon sensing viral dsRNA

Question 12

How does viral dsRNA occur during herpes virus infections?

Answer 12

Herpes virus dsDNA encodes genes on the top and bottom strand. When they are bidirectionally transcribed it creates complementary mRNA transcripts that can associate to form dsRNA

Question 13

What 2 proteins do herpesviruses possess to prevent deactivation (dephosphor.) of elF2a. Describe the mechanism of each

Answer 13

US11: mops up dsRNA, preventing activation of PKR and subsequent phosphorlyation of elF2a
Gamma34.5: binds to cellular phosphatase PP1, guiding it to elF2a to dephosphorylate

Question 14

Why do herpesviruses need to combat phospharylation of elF2a?

Answer 14

Because elF2a needs to be dephosphorylated to allow ternary complex formation and initiation of translation

Question 15

List the 3 proteins herpesviruses use to facilitate initiation of translation/competition for translation machinery and each ones function

Answer 15

US11: dsRNA mop, prevents: activation of PKR, subsequent phosphorlyation of elF2a by PKR and blockage of ternary complex formation

Gamma 34.5: binds cellular PP1, guiding it to elF2a to dephosphorylate it and allow ternary complex formation

VHS: virion host shutoff, endoribonuclease that selectively degrades host mRNA, giving viral mRNA priority access to host translation machinery

Question 16

What type of bulk transport is used for herpesvirus egress?

Answer 16

Exocytosis

Question 17

Describe the structure and composition of herpesvirus nuclear egress complex. What method was used to visualize it experimentally?

Answer 17

Hexagonal lattice structure made up of 2 viral proteins/ Visualized with cyro-EM