http://news.yahoo.com/s/hsn/20080229...edmorethanonce
FRIDAY, Feb. 29 (HealthDay News) -- A gene in Asian monkeys that may have evolved as protection against a group of viruses that includes HIV has been identified by Harvard Medical School researchers, who add that their finding suggests the current AIDS epidemic is not a new kind of scourge.
The TRIM5-CypA gene found in Asian macaques is a hybrid of two existing proteins, TRIM5 and CypA. This combination creates a single protein that blocks infections by lentiviruses.
This is the second time a TRIM5-CypA hybrid gene has been identified in monkeys. The other one -- TRIMCyp -- was found in South American owl monkeys in 2004. But it's not likely that these two gene combinations arose from a single common ancestor, the Harvard researchers said.
TRIM5-CypA wasn't found in monkey closely related to the Asian macaques and TRIMCyp wasn't found in any other South American primate species. This suggests that the two combination genes evolved separately, once in the macaques and once in the owl monkeys.
This development of similar genetic adaptations in different species is called convergent evolution. A prime example is the development of flight in bats and in birds.
The fact that adaptations involving TRIM5 and CypA occurred at least twice in primates suggests that this combination provided a strong evolutionary advantage, the Harvard researchers said.
It may be possible that the combination genes developed to prevent infection by prehistoric viruses related to modern HIV, they suggested. If this is true, it could mean that an AIDS-like epidemic is not unique to the current time, and such outbreaks may have afflicted the primate ancestors of humans.
The study is published in the Feb. 29 issue of PLoS Pathogens.
Monkey Gene That Blocks AIDS Viruses Evolved More Than Once 
Linear Mode
