Structure of HIV genome 'decoded'
Scientists say they have decoded the entire genetic content of HIV-1 - the main cause of Aids in humans.
They hope this will pave the way to a greater understanding of how the virus operates, and potentially accelerate the development of drug treatments.
HIV carries its genetic information in more complicated structures than some other viruses.
The US research, published in Nature, may allow scientists the chance to look at the information buried inside.
HIV, like the viruses which cause influenza, hepatitis C and polio, carries its genetic information as single-stranded RNA rather than double-stranded DNA.
The information enclosed in DNA is encoded in a relatively simple way, but in RNA this is more complex.
We are also beginning to understand tricks the genome uses to help the virus escape detection by the human host
Ron Swanstrom
Study author
RNA is able to fold into intricate patterns and structures. Therefore decoding a full genome opens up genetic information that was not previously accessible, and may hold answers to why the virus acts as it does.
The team from the University of North Carolina at Chapel Hill said they planned to use the information to see if they could make tiny changes to the virus.
"If it doesn't grow as well when you disrupt the virus with mutations, then you know you've mutated or affected something that was important to the virus," says Ron Swanstrom, professor of microbiology and immunology.
"We are also beginning to understand tricks the genome uses to help the virus escape detection by the human host."
Deep inside
Dr David Robertson from the University of Manchester welcomed this "definitive analysis".
"What this may reveal is some of the proteins operating at a level below the structures, which may have all sorts of functions within the virus.
"More generally, if we can unpick the structures then we can compare the systems of different viruses and gain new understanding of how they work."
Keith Alcorn of the HIV information service NAM added: "Encouraging the virus to mutate is not a new idea, but it is one of a number of options on the table.
"How important this information will be for the development of new drugs remains to be seen, but it is a useful addition to what we know."
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Monkey viruses 'created HIV'
Two different strains of a virus affecting monkeys probably combined to create the form of HIV which has spread around the world, say scientists.
They believe the two strains of Simian Immunodeficiency Viruses (SIVs) first came together in chimpanzees who had eaten monkeys carrying the different strains.
The viruses' DNA then merged, creating a new form - the forerunner of HIV-1.
This was then passed to humans - possibly through the handling of contaminated chimpanzee flesh.
The theory has been put forward by a team from Nottingham University, who carried out an extensive genetic analysis of SIV strains.
In particular they focused on a strain called SIVcpz, which is found in chimpanzees and which has previously been shown to be closely linked to HIV-1.
In some ways, SIVcpz was found to resemble SIVrcm, a virus endemic in red-capped mangabeys.
But in other respects it closely matched another form of the virus, SIVgsn, which is found in the spot-nosed monkey.
Chimpanzees are known to hunt and eat both species of monkey.
Cross-species transmission
Writing in the journal Science, the researchers said: "Because chimpanzees are known to hunt smaller monkey species, the simplest explanation appears to be that both SIVrcm and SIVgsn have been acquired by chimpanzees and recombined in that host."
They said the finding was important evidence that another primate species besides humans acquired SIV by cross-species transmission under natural conditions.
Last year French researchers found that SIVgsn contained a particular gene which gave it the potential to jump from monkeys to man.
The Nottingham researchers also warn that because of the similarity between chimpanzees and humans, any virus that successfully adapts to spreading among chimpanzees would be a candidate for a further jump to humans - a potential new strain of HIV.
Exactly how SIVcpz was transmitted to humans to re-emerge as HIV is not known.
One theory is that "bush meat" consumption may have been to blame.
If people had cut themselves while preparing infected meat, they could have acquired the virus.
SIVs are a large family of viruses, carried by many species of monkeys in Africa, but chimpanzees are the only apes known to be naturally infected.
Source: BBC
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