31. Retroviruses 3

Question 1

inherent ability of mature capsid proteins to _______

Answer 1

inherent ability of mature capsid proteins to ASSEMBLE

Question 2

2 main enzymatic activities of RT

Answer 2

1. polymerase
2. nuclease

Question 3

what is the name of the polymerase subunit of RT?

Answer 3

p66

Question 4

what is the name of the nuclease subunit of RT?

Answer 4

p51

Question 5

does polymerase of RT use RNA or DNA as a template?

Answer 5

can use either RNA or DNA

Question 6

nuclease activity of RT?

Answer 6

cleaves RNA-DNA hybrid

Question 7

how is p51 made?

Answer 7

made from p66 from proteolytic cleavage

Question 8

what 2 things does RT require to start transcription?

Answer 8

1. template (genome RNA)
2. primer

Question 9

what is the primer in retroviruses?

Answer 9

host cell tRNA

Question 10

First step of RT activity

Answer 10

RT starts at 3’ end of tRNA and copies RNA template until 5’ end into cDNA with RdDP activity

Question 11

where does RT activity occur?

Answer 11

occurs within core during transit and is completed in nucleus

Question 12

how does the virus acquire tRNA from the host?

Answer 12

may be pre-initiation transcription during assembly that allows tRNA to enter core

Question 13

Second step of RT activity (once cDNA is made)

Answer 13

RT destroys the original genomic RNA with nuclease activity

Question 14

Third step of RT activity (once RNA is destroyed)

Answer 14

cDNA jumps to the 3’ end of viral RNA via direct repeats to make minus strand DNA

Question 15

describe the direct repeats

Answer 15

complementary sequences at 5’ and 3’ ends of the viral RNA, also allow for integration

Question 16

Fourth step of RT activity (as -DNA synthesis proceeds)

Answer 16

nuclease activity of RT degrades viral RNA –> RNAse activity

leaves POLYPURINE TRACT

Question 17

function of polypurine tract

Answer 17

acts as primer for +DNA synthesis and maintains its hybridization even when RNAse activity

Question 18

Fifth step of RT activity (after RNAse activity)

Answer 18

polypurine tract acts as primer to make +DNA

Question 19

Sixth step of RT activity (after +DNA synthesis)

Answer 19

tRNA is removed, leading to translocation of new +DNA to bind to -DNA strand via PBS and allow continued +DNA synthesis

Question 20

2 types of RT inhibitors

Answer 20

1. NRTIs
2. NNRTIs

Question 21

diff btwn NRTI and NNRTI

Answer 21

NRTI acts as nucleoside to block RT

NNRTI covalently binds RT to block its activity

Question 22

how does RT gain resistance?

Answer 22

bc of errors

Question 23

2 functions of integrase

Answer 23

1. 3’ processing
2. strand transfer

Question 24

3 steps of integrase activity

Answer 24

1. 2 integrase enzymes bind 2 LTRs on each end of the new dsDNA and start translocation to nucleus
2. integrase performs 3’ processing, removing 2 bp to expose 3’ OH for ligation with host DNA (i.e. makes a nick)
3. free 3’ OH groups attack host DNA at random location for strand transfer to insert viral genome into host

Question 25

example of integrase inhibitor

Answer 25

Raltegravir

Question 26

another name for integrase inhibitors

Answer 26

integrase strand transfer inhibitors

Question 27

why are integrase inhibitors known as integrase strand transfer inhibitors?

Answer 27

they bind active site of integrase, therefore interfering with strand transfer

Question 28

how does raltegravir work?

Answer 28

prevents formation of covalent bonds btwn host and virus DNA by interfering with divalent cations in enzyme's catalytic core

Question 29

what is a requirement of integrase inhibitor?

Answer 29

must be able to penetrate infected cell and nucleus

Question 30

HIV protease assembles as:

Answer 30

HIV protease assembles as dimer

Question 31

what does HIV protease do?

Answer 31

cleaves precursor Gag and Gag/Pol proteins

Question 32

where do protease inhibitors act?

Answer 32

on enzymatic site