32. Retroviruses 4 Flashcards
(39 cards)
what elements regulate splicing?
RNA cis-acting sequences bound by host factors
what are the 2 sizes of spliced mRNAs?
4kb and 2kb
2 types of RNA cis-acting elements
- exon splicing silencers
- exon splicing enhancers
locations of splice sites?
1 splice site on 5’ end, the rest are further downstream
4 examples of host TFs that bind transcription cis-acting elements in promoter region?
- TATA
- AP1
- NFkB
- Sp1
why do host TFs bind transcription cis-acting elements?
to enhance transcription
what is Tat and its 2 roles?
Tat = transactivating protein
- initiates transcription
- promotes elongation
how does Tat enhance transcription + elongation?
recruits CycT and Cdk9 TFs
what is the role of REV? how does it work?
REV promotes mRNA export from the nucleus by concatemerizing with RNA REV response element
where is the RNA REV response element found?
found in the envelope coding region, therefore found in 4kb mRNA but absent in 2kb mRNA
describe the 3 steps for rev and tat activity
- the spliced 2kb mRNAs for REV, TAT, and NEF are exported to cytoplasm to be translated
- REV goes back to nucleus to bind RRE and bring out 4kb mRNA
- TAT goes back to nucleus to increase transcription
what is the role of auxillary/accessory proteins?
for defense, enhance viral replication, etc.
what is Vif?
promotes degradation of APOBEC3 restriction factor to block APOBEC3 antiviral function
what is APOBEC3 antiviral function?
APOBEC3 associates with Gag and gets packaged –> creates errors in expression, leading to hypermutation
how does APOBEC3 create errors in expression?
deaminates cytidine to make uridine
what does APOBEC3 stand for?
APOlipoprotein B Editing Complex protein
what are considered to be early events in retroviral replication cycle?
everything up to integration
what are considered to be late events in retroviral replication cycle?
after integration, everything after transcription
what does Vpu do in HIV1?
counteracts tetherin restriction factor
what does tetherin do?
makes virions bind to PM or each other to prevent release of virions
How is tetherin counteracted in SIV?
With Nef protein
How is tetherin counteracted in HIV2?
With envelope protein
what is required for tetherin to exert its function?
must function as a dimer
how does Vpu target tetherin?
Vpu targets tetherin for degradation via proteasomal and lysosomal degradation pathways
