Monkey gene called Trim 5 alpha offers clue to HIV origin in humans:-

The human form of the gene has what appears to be the crucial difference of just one amino acid from that of the &to=http://english.pravda.ru/science/19/94/377/13706_monkey.html' target=_blank>rhesus monkey . So it shows that rhesus monkeys can be infected by a monkey form of HIV, SIV (simian immunodeficiency virus), but not by HIV itself.

British researchers reported in the paper published in the journal Current Biologythey that they had identified a gene that could prevent the rhesus monkey from getting infected by the &to=http://english.pravda.ru/main/2001/06/05/6956.html' target=_blank>HIV virus.