Retroviruses Flashcards
What is the basic structure of a retrovirus?
+ ssRNA, enveloped
What conferes specificity of infection>
Transmembrane glycoproteins that mediate attachment to host receptors
What is carried in a retrovirion?
2 copies of + ssRNA, 50 copies of reverse transcriptase and integrase
Where does integration occur?
in the long-terminal repeats of several hundred base pairs found at both 5’ and 3’ ends of the RNA
What are the three major coding regions and what do they code for?
Gag: core proteins
Pol: reverse transcriptase, integrase and protease (RNase H)
Env: surface glycoproteins - determine viral tropism
How is the genome transcribed?
Single polycistronic mRNA transcript –> differential splicing for expression
-can be cleaved by proteolytic ensymes to form several proteins
What are the two main forms of retroviruses?
Exogenous: descrete viral particles that are transmitted from host to host
Endogenous: intrinsic part of host genome
What 3 circumstances allow a retrovirus to become an oncogenic virus?
1) Incorporate an oncogene into its genome
2) Insertion of viral genome adjacent to a cellular oncogene
3) Transforming cell by expression of transactivating proteins
What non-retrovirus uses reverse transcriptase?
HepB virus (partially ds circular DNA) uses RT and RNA intermediates as part of lifecycle
Name the 4 known retroviruses that cause disease in humans
Human T-cell leukemia viruses (HTLV I and II): delta retroviruses
HIV-1 and 2: lentiviruses
What is the significance of human endogenous retroviruses (HERVS)?
Compse 8% of human genome
Not capable of replication
Indicated in autoimmune diseases
How does HTLV-1 transmission occur?
Via infected lymphocytes, not through free virus
Blood transfusion, sexual contact, and vertical via placenta or lymphocytes in breast milk
What is the primary infected cell of HTLV-1?
CD-4 T lymphocytes
doesn’t kill the T cells like HIV does; merely causes imbalance between Th1 (way too many) and Th2 cells
How does HTLV1 cause cancer?
Poorly understood: does NOT encode an ocogene and doesn’t have constent integration site
What two HTLV-1 genes regulate Tcell proliferation?
Tax and Rex: activate expression of IL-2 and IL-2r