31. Retroviruses 3 Flashcards
inherent ability of mature capsid proteins to _______
inherent ability of mature capsid proteins to ASSEMBLE
2 main enzymatic activities of RT
- polymerase
- nuclease
what is the name of the polymerase subunit of RT?
p66
what is the name of the nuclease subunit of RT?
p51
does polymerase of RT use RNA or DNA as a template?
can use either RNA or DNA
nuclease activity of RT?
cleaves RNA-DNA hybrid
how is p51 made?
made from p66 from proteolytic cleavage
what 2 things does RT require to start transcription?
- template (genome RNA)
- primer
what is the primer in retroviruses?
host cell tRNA
First step of RT activity
RT starts at 3’ end of tRNA and copies RNA template until 5’ end into cDNA with RdDP activity
where does RT activity occur?
occurs within core during transit and is completed in nucleus
how does the virus acquire tRNA from the host?
may be pre-initiation transcription during assembly that allows tRNA to enter core
Second step of RT activity (once cDNA is made)
RT destroys the original genomic RNA with nuclease activity
Third step of RT activity (once RNA is destroyed)
cDNA jumps to the 3’ end of viral RNA via direct repeats to make minus strand DNA
describe the direct repeats
complementary sequences at 5’ and 3’ ends of the viral RNA, also allow for integration
Fourth step of RT activity (as -DNA synthesis proceeds)
nuclease activity of RT degrades viral RNA –> RNAse activity
leaves POLYPURINE TRACT
function of polypurine tract
acts as primer for +DNA synthesis and maintains its hybridization even when RNAse activity
Fifth step of RT activity (after RNAse activity)
polypurine tract acts as primer to make +DNA
Sixth step of RT activity (after +DNA synthesis)
tRNA is removed, leading to translocation of new +DNA to bind to -DNA strand via PBS and allow continued +DNA synthesis
2 types of RT inhibitors
- NRTIs
- NNRTIs
diff btwn NRTI and NNRTI
NRTI acts as nucleoside to block RT
NNRTI covalently binds RT to block its activity
how does RT gain resistance?
bc of errors
2 functions of integrase
- 3’ processing
- strand transfer
3 steps of integrase activity
- 2 integrase enzymes bind 2 LTRs on each end of the new dsDNA and start translocation to nucleus
- integrase performs 3’ processing, removing 2 bp to expose 3’ OH for ligation with host DNA (i.e. makes a nick)
- free 3’ OH groups attack host DNA at random location for strand transfer to insert viral genome into host
example of integrase inhibitor
Raltegravir
another name for integrase inhibitors
integrase strand transfer inhibitors
why are integrase inhibitors known as integrase strand transfer inhibitors?
they bind active site of integrase, therefore interfering with strand transfer
how does raltegravir work?
prevents formation of covalent bonds btwn host and virus DNA by interfering with divalent cations in enzyme’s catalytic core
what is a requirement of integrase inhibitor?
must be able to penetrate infected cell and nucleus
HIV protease assembles as:
HIV protease assembles as dimer
what does HIV protease do?
cleaves precursor Gag and Gag/Pol proteins
where do protease inhibitors act?
on enzymatic site
