Lecture 7 - DNA Viruses: Papova 1

Question 1

Eukaryotic mRNA is mono or polycistronic?

Answer 1

Monocistronic

Question 2

Define monocistronic and polycistronic mRNA

Answer 2

Monocistronic mRNA: single open reading frame for one protein

Polycistronic mRNA: multiple open reading frames for multiple proteins

Question 3

What does it mean for different ORFs to be in the same frame?

Answer 3

They have different start codons but the same stop codon

Question 4

What 2 virus families does papovaviridae comprise?

Answer 4

Papillomaviridae

Polyomaviridae

Question 5

Describe the morphology and genome of Papovaviridae

Answer 5

Nonenveloped, covalently closed circular dsDNA viruses

Question 6

Describe the capsid structure of SV40 (3)

Answer 6

Structural unit: VP1 pentamer

Capsid: icosahedron of 72 VP1 pentamers

Question 7

What is the receptor for SV40 and what does binding initiate?

Answer 7

Receptor is a glycosphingolipid, binding to it activates cellular tyrosine kinases and triggers actin filament reoganization and internalization

Question 8

Describe the steps in SV40 entry (APU) (4)

Answer 8

1) Ganglioside receptor binding triggers internalization by caveolin-dependent endocytosis
2) Caveosome brings virions to the ER via a sorting vesicle
3) virions are released from the ER into the cytoplasm by an unknown mechanism
4) Capsid docks the nuclear pore complex and disrupts nuclear envelope and lamina organization

Question 9

SV40 has a small genome, how does it produce large amounts of different proteins at different times and in different quantities? List 4 strategies they employ and the stage of MMS it occurs (transcr. etc.)

Answer 9

Transcription: differential regulation of promoters
Post transcription: alternative splicing (poly-adenylation)
Translation: leaky scanning
Post-translation: micro RNA regulation

Question 10

What is the mechanism of action of SV40s enhancer region to promote transcription?

Answer 10

Enhancer promotes a nucleosome-free region allowing RNA polymerase binding

Question 11

SV40 gene expression can be divided into 2 phases. What are they and when do they occur?

Answer 11

Early phase: before vDNA replication

Late phase: after vDNA replication

Question 12

How many promoters does SV40 genome have?

Answer 12

2, early promoter and later promoter

Question 13

What is the SV40 early gene product? What does it promote and inhibit?

Answer 13

Large T antigen:
Promotes: S phase induction, late gene transcription and vDNA replication
Inhibits: early gene transcription

Question 14

What type of proteins are the SV40 late gene products?

Answer 14

Structural proteins

Question 15

What is the regulatory region of SV40 genome called?

Answer 15

Ori

Question 16

What are the 2 promoters located in the SV40 Ori? What do they make?

Answer 16

Early promoter: T antigen

Late promoter: structural proteins

Question 17

What is the directionality of the 2 promoter elements in Ori?

Answer 17

Early and late promoters are transcribed in opposite directions

Question 18

The first step in SV40 gene expression involves production of ___ antigen by basal ___ factors.

Answer 18

First step in SV40 gene expression involves production of T antigen by basal transcription factors

Question 19

The ___ region of SV40 genome facilitates transcription initiation of the early genes encoding ___ by preventing ___ formation, thereby stimulating RNA polymerase binding

Answer 19

The enhancer region of SV40 facilitates transcription initiation of the early genes encoding T antigen by preventing nucleosome formation, thereby stiulating RNA polymerase binding

Question 20

The second step in SV40 gene expression is early gene mRNA splicing to make ___ and ___

Answer 20

SV40 early gene mRNA is spliced to make large T antigen and small T antigen

Question 21

In the third step of SV40 gene expression, TAg interacts with host factors ___ and ___ to induce ___ phase

Answer 21

TAg interacts with host factors Rb and p53 to induce S phase

Question 22

In the fourth step of SV40 gene expression, hexamers of what bind to the Ori?

Answer 22

TAg hexamers

Question 23

What are the 3 functions of large T antigen when bound to the Ori of SV40?

Answer 23

• increase vDNA synthesis
• increase late gene expression
• decrease early gene transcription

Question 24

TAg is an early gene product. When it binds to the Ori it decreases early gene expression. What form of regulation is this?

Answer 24

Autoregulation

Question 25

How does TAg directly increase late gene expression?

Answer 25

TAg hexamerizes at the Ori and stabilizes transcriptional complexes for late genes

Question 26

In the fifth step of SV40 gene expression, increased ___ concentration titers out a repressor of ___ promoter, allowing for expression of ___ genes

Answer 26

Increased vDNA concentration titers out a repressor of the late promoter, allowing for expression of late genes

Question 27

How is repression of the late promoter for SV40 removed?

Answer 27

High viral DNA concentration titrates out the repressor of the late promoter (more promoters than there are repressors)

Question 28

What are 2 reasons that alternative splicing of viral pre-mRNA is important for viruses?

Answer 28

• expands the coding capacity of their genome

- deals with the monocistronic constraint of euaryotic translation machinery

Question 29

What are 2 ways in which LTAg assists in replication of SV40 vDNA?

Answer 29

• acts as helicase to unwind DNA

- binds Topoisomerase 1 to relieve positive supercoils