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HIV/Retroviruses
Overview of the molecular biology of HIV as an example of retroviruses
| Question | Answer |
|---|---|
| What is the viral receptor for HIV? | CD4 |
| What are the co-receptors for HIV? | -CCR5 (macrophages) -CXCR4 (CD4+ T cells) |
| Does HIV have a maturation step in its life cycle? | Yes |
| What is contained in the mature viral particle? | A capsid containing: -2 copies of the genome covered by a nucleocapsid -Reverse transcriptase -integrase |
| What are the three main genes of HIV? | -Gag -Pol -Env |
| What does Gag encode? | Structural proteins |
| What does Pol encode? | Enzymes including the RT, protease, and integrase |
| What does Env encode? | The receptor ligand |
| How is the Gag-Pol protein produced? | By -1 ribosomal frameshift |
| Env is in the same reading frame as Gag-Pol. How is Env produced? | Alternative splicing |
| What shape is the capsid? | Conical |
| How are Env and Vpu obtained? | Leaky scanning |
| What is the overall architecture of the HIV promoter region? | 5'-U3-R-U5-3' |
| What is the function of U3? | Contains the viral promoter |
| What is the function of R? | Contains the polyA signal |
| What is the function of U5? | Contains the binding sites of transcription factors |
| What are the steps of the replication cycle ? | -Entry -Reverse transcription -Integration -Transcription/translation -Assembly -Budding -Maturation |
| What are the steps of receptor attachment? | -Attachment and CD4 binding -Co-receptor binding -Membrane fusion |
| What three things must occur for successful HIV entry? | -Lipid mixing -Endocytosis -Content mixing |
| What does HIV use as a primer for the reverse transcription of its genome? | A host endogenous tRNA (Lys) |
| What happens once the RT reaches the 5' end of the RNA template? | RNAse H degrades the already reverse transcribed gRNA, creating a 3' overhanging DNA that is complementary to the other end of the RNA |
| What happens after RNAse H creates a 3' overhang during reverse transcription? | The two complementary R sequences base pair and reverse transcription continues. |
| What section of the gRNA is not degraded and can act as a primer for (+) DNA production? | The poly purine tract (PPT) |
| Where does reverse transcription take place? | In the cytosol |
| What is the pre-integration complex? | The proviral DNA in complex with the integrases and other factors that will enable integration |
| What is the function of LEDGF/p75? | To bind to chromatin, putting the PIC in proximity to the chromatin |
| What is autointegration? | When proviral DNA is inserted into itsself |
| What is the Trans-activation response element (TAR)? | A sequence in the proviral DNA that recruits TAT |
| What is TAT? | An endogenous host protein that gives RNAP its processivity and recruits kinases of the CTD |
| Does HIV use Leaky scanning? | Yes. Leaky scanning is used to access a second reading frame to transcribe Env |
| What is Rev? | A protein critical for export of mRNAs out of the nucleus |
| What is RRE? | Rev response element. Sequence in mRNA that binds Rev |
| What is DLS? | Dimer linkage site. Site of dimerization of the genome that is to be packaged in the viral particles. |
| What is the Psi sequence? | A sequence essential for packaging, binds the nucleocapsid |
| Where are gammaretroviruses found? | As endogenous retroviruses in several species including mice and humans |
| What molecular biology technique do gammaretroviruses use? | Suppression of termination |
| What is an ecotropic retrovirus? | A retrovirus that infects only mice cells |
| What is a xenotropic retrovirus? | A retrovirus that infects species other than mice |
| What is a polytropic retrovirus? | A retrovirus that can infect many species, mice included |
| What is an amphotropic retrovirus? | A retrovirus that can infect many species, but uses a different receptor than that of polytropic retroviruses |
| What receptor do ecotropic retroviruses use? | CAT-1 |
| What receptor do xenotropic retroviruses use? | XPR1 |
| What receptor do polytropic retroviruses use? | XPR1 |
| What receptor do amphotropic retroviruses use? | Pit2 |
| What are 3 ways in which retroviruses can cause cancer? | -By carrying a viral oncogene -By inserting into and disrupting a gene important for preventing cancer -By disregulating the expression of a proto-oncogene |
Created by:
mbell133
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