Saturday, October 17, 2009
A Primer on XMRV
XMRV is a retrovirus - a virus that uses its RNA to copy its genetic material into host DNA. The best known retrovirus is HIV (Human Immunodeficiency virus) - the virus that causes AIDS. XMRV is only the third such retrovirus discovered to infect humans, after the discovery of HTLV. Like HIV, XMRV has 3 genes in common - gag, pol, and env. The gag gene encodes the capsid and matrix proteins, the pol gene encodes a single protein which is cleaved into three separate proteins by the viral protease - reverse transcriptase, viral protease, and integrase, and the env gene encodes the envelope glycoproteins. The XMRV also contains an androgen response element gene, which I will discuss a theoretical role in a future post. The XMRV genome is somewhat smaller than the HIV genome - 8161 base pairs as opposed to ~9500 base pairs in the HIV genome. Based on initial findings, it appears that XMRV infects the immune system in ways that are all too familiar in HIV. The envelope glycoproteins likely bind to some yet unknown immune system protein like HIV binds to the CD4 receptor, and co-receptor, possibly CD8, CD 16 or CD 56 on the surface of NK cells.