Retroviruses Flashcards
(29 cards)
What are the kinds of infections caused by retroviruses?
no illness
tumors
wasting diseases, neurological
immune deficiencies (HIV)
Properties of retroviruses
acquire host cell sequences that could be oncogenes
integrate into host cell chromosomes
fast genome evolution
retroviruses’ structure
enveloped with envelope proteins in membrane, matrix proteins underneath lipid bilayer
capside of structural proteins
2 copies of + sense ssRNA
core can be differently shaped
How is retroviral genomic RNA made?
by host’s polymerase II
Retrovirus genomic RNA composition
from 5' to 3': 5'cap R: repeat U5: unique for 5 end gag gene: encodes polyprotein consisting of matrix, capsid, nucleocapsid, and protease
pol (polymerase) gene: reverse transcriptase, integrase
env (envelope) gene: encodes env protein which gets cleaved to surface (SU) and transmembrane (TM) portions
U3: unique for 3’ end
R: second repeat
3’ poly A tail
Difference btwn simple retrovirus and complex?
Complex retrovirus does alternative splicing with additional genes; simple only splices once
replication cycle of retrovirus
adsorption penetration, uncoating reverse transcription goes into nucleus integrates into host DNA viral RNA synthesis using host pol II RNA processing virion protein synthesis assembly and buds capsid matures
What steps of replication cycle does retrovirus use host cell machinery a lot?
after integration
How does retrovirus bind cell?
envelope protein and host cell receptor
What is used to convert ssRNA to dsRNA for the retrovirus?
reverse transcriptase
Does HIV genome get into the nucleus?
Yes
How is the ssRNA genome from the retrovirus different from the dsRNA provirus?
dsRNA provirus is longer than template RNA b/c it contains U3 and U5 duplicated at ends to make LONG TERMINAL REPEATS (LTRs)
Reverse transcriptase has two polymerase activities. Name them
RNA dependent DNA polymerase
DNA dependent DNA polymerase
What explains the rapid evolution of the retrovirus genome?
reverse transcriptase makes 5 errors per genome
What is a very important target for antiviral drugs against HIV?
reverse transcriptase
Where does integrase choose to integrate the retrovirus dsDNA?
it is not specific–insertion occurs at random
What does integrase recognize with the retroviral DNA?
ends of U3 and U5
How long does the integrated retroviral DNA stay in the host cell’s DNA?
forever
What is the major role of the long terminal repeat in retroviral DNA?
directs viral RNA synthesis because U3 has sites for cellular transcription factors
Why is HIV active in activated T cells?
activated T cells have the transcription factor NFkB, which the HIV LTR needs
In what kinds of retroviruses does splicing of envelope mRNA occur?
all retroviruses
Why is targeting mRNA splicing in retroviruses not good?
host cell also uses the machinery for splicing
How is gag-pol of the retrovirus translated?
ribosomes ignore the gag stop codon and go on to the end of pol
What cleaves the original envelope protein of retroviruses into two smaller fragments?
protease
