Control Of Virus Replication - DNA Viruses

Question 1

What are the problems that DNA viruses face?

Answer 1

Synthesis of DNA usually only occurs in S phase
Problem of shortening of linear DNA genomes

Question 2

What do DNA viruses have to do due to S phase synthesis?

Answer 2

most cells in our body are not replicating - viruses have to trigger the cell to go back through the cell cycle into synthesis phase

Question 3

Why are DNA viruses associated with cancer but not RNA viruses?

Answer 3

Because DNA viruses have to trigger cells to go back thorugh cell cycle into synthesis phase which can lead to cancer

Question 4

What are examples of DNA viruses?

Answer 4

Pox viruses
Herpesviruses
Adenoviruses
Papillomaviruses

Question 5

What is the exception of DNA virus replication in the nucleus?

Answer 5

Poxviruses
They carry their polymerase required for DNA replication so they replicate in the cytoplasm

Question 6

What is an example of a virus-encoded transcpirotn factor for HSV?

Answer 6

HSV-1 VP16 (alphaTIF)

Question 7

What do virus encoded trasncpirotin factors do?

Answer 7

Binds cellular transcpriotn factors to activate immediate early genes

Question 8

What phase of the cell cycle are most cells that viruses affect?

Answer 8

G0 phase

Question 9

What is normally the case in G1 phase?

Answer 9

Transcription factor E2F is bound tightly to retinoblastoma protein

Question 10

What needs to happen to get into S phase?

Answer 10

They need to disrupt the interaction between retinoblastoma protein and E2F and E2F will trigger transcription

Question 11

What causes the trigger between G1 and S phase?

Answer 11

Phosphorylation of proteins by cyclin dependent kinases

Question 12

How do viruses affect cyclin dependent kinases?

Answer 12

Some viruses make their own cyclin proteins that mimic host proteins that impact CDKs
Some viruses switch on signalling pathways to cause production of host cyclin D

Question 13

What role do p53 and p21 have?

Answer 13

They have a strong regulatory role
P53 influences p21 which switches off CDKs

Question 14

What do viral proteins do to p53?

Answer 14

Block it hence allowing unregulated CDK activation

Question 15

What does adenovirus protein E1A do?

Answer 15

Block CDK inhibitors

Question 16

What does SV40 large T act on?

Answer 16

Rb and p53

Question 17

What happens when you get into S phase?

Answer 17

Lots of ribonucleotides synthesis genes are switched on
Rb and E2F become dislocated, dNTPs get made

Question 18

What are the two ways of viral DNA replication?

Answer 18

Classical DNA replication or displacement synthesis

Question 19

What is the problem with classical replication in virus genomes?

Answer 19

You need primers and without adding bits of DNa back on to make primer binding sites, every replication cycle, the genome would get slightly shorter

Question 20

What type of virus has classical synthesis and why?

Answer 20

Polyomavirus SV40
Because it has a circular genome

Question 21

How does initiation of SV40 replication occur?

Answer 21

Binding of helicases enzymes
Binds to an origin of replication, unwinds DNa, open up foot of replication bubble
Have one subunit in one direction, the other in the other direction
Eventually they go all the way round and hit each other and fall off because they are circular

Question 22

What is the key difference between adenovirus and SV40 replication?

Answer 22

There are proteins attached to the end of the DNA molecule to avoid the end problem

Question 23

What happens in adenovirus replication?

Answer 23

DNA binding protein binds to one strand, has specificity for a motif on positive strand, this unzips DNa, now have a protein on one strand and another protein on the other strand

Question 24

What happens when adenovirus polymerase binds to one strand?

Answer 24

DNTPs come along ad that gets to this junction where DP isn’t captured, this is why it is called displacement synthesis. Now the polymerase will push this zippered DNA apart

Question 25

Is DNA produced in two directions or one in displacement synthesis?

Answer 25

One direction only

Question 26

What happens in displacement synthesis now there is a dead strand of DNa not being replicated?

Answer 26

The ends of the ss piece of DNa are complementary to each other so they stick together
Form a pan handles structure
This acts as a primer for synthesis of another positive strand

Question 27

What cells does herpes simplex virus infect?

Answer 27

Epithelial cells

Question 28

In HSV-1 genome, it has two segments, how many different genome rearrangement possibilities are there?

Answer 28

4 as both segments can be inverted

Question 29

What are the 4 alpha, early immediate genes to remember for HSV-1 genome?

Answer 29

ICP0
ICP4
ICP22
ICP27

Question 30

What does ICP0 do?

Answer 30

Potent transactivator of gene expression

Question 31

What does ICP4 do?

Answer 31

Positive regulation of intermediate and late genes

Question 32

What does ICP22 do?

Answer 32

Regulates expression of ICP0

Question 33

What does ICP27 do?

Answer 33

Negatively regulates alpha genes and upregualtes late genes

Question 34

What does binding and entry of HSV-1 virion require interaction with to start?

Answer 34

Heparin sulfate and HVEM, and nectin

Question 35

What do LATs do?

Answer 35

Trigger virus replication to go from productive stage into latent stage