Ch. 7 Reverse Transcription and Integration Flashcards
(23 cards)
Where does the name retrovirus come from?
The retrograde flow of information
Reverse Transcriptase needs a ______ to initiate DNA synthesis.
specific primer
Retroviral particles contain ___ copies of the genome. This complex also includes two molecules of ____. What is their purpose?
two; they are held together by multiple regions of base pairing at the 5’ end sequences. tRNA. They serve as a primer.
Where does the tRNA bind?
the primer binding site (pbs) near the 5’ end of the RNA genome.
What are the activities of RT?
RNA dep. and DNA dep. DNA synthesis; DNA unwinding; hydrolysis of RNA in RNA-DNA hybrid by RNase H.
What is the purpose of RNAse H?
It degrades genomic RNA template strand after DNA comp. strand has been synthesized.
How is the (-) strand of DNA initiated? What is the initiation piece of DNA called?
Retroviral transcription starts near the 5’ end of the genome. This small segment of DNA is synthesized from RNA template, and then corresponding RNA is degraded;
(-) Strong Stop DNA
Complementary pieces of (-)strong stop DNA and 3’ end of genomic RNA engage. This is called:
The first template exchange
DNA is then synthesized all the way to the 5’ end of the template strand. RNase digests the RNA template strand, leaving chunks of RNA called:
What do these act as? What is the name of the resulting DNA?
Polypurine tracts. These act as primers
(+) Strong Stop DNA results, and the DNA template exchange occurs to allow synthesis of remaining (+) strand DNA. (+) Strong Stop DNA
The final product is:
A linear DNA duplex copy of the viral genome.
RT is encoded by:
pol genes.
What is the class of protein for RT?
a heterodimer. Only one subunit has RNase H activity.
What is the speed of RT?
SLOW…. 1-1.5 nucleotides/second. 10X slower than DNA dep. DNA pol. It takes HIV 4 hours to copy its genome after infection.
Where does DNA synthesis take place?
The cytoplasm, in a subviral complex called an RT complex.
What would be a good target for fighting AIDS?
Reverse transcriptase; also integrase
Subunits of RT dimer are structurally:
asymmetric.
How many Reverse Transcriptases are typically present in a retroviral particle (virion)
50-100 copies.
Why is there a high rate of mutation in retroviruses?
Lack of proofreading. 1 error per 10^4 nucleotides. For HIV this means one lesion per genome per cycle.
What allows for insertion of DNA product into host DNA? What is the name for this new viral DNA?
integrase (IN);
Proviral DNA
Where is Integrase encoded?
the 3’ End of the RT pol gene. It is produced by viral protease processing of Gag-Pol
When integrated, how many base pairs of the virus are cropped? What happens to the host DNA?
What is also present?
2 from each side. ;
There is a short duplication so host DNA is the same on both sides of proviral DNA;
Short, inverted repeats at the termini
What is the structure of Integrase?
It exists in monomeric, dimeric and tetrameric forms in absence of DNA substrate. The tetramer is stabilized by interaction with a pair of DNA ends
How does integrase work?
Nicking of host DNA and then addition of viral DNA. Host senses damage and “repairs” DNA
