Now, a machine that sequences single molecules of DNA

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London, April 7 : Massachusetts-based company Helicos BioSciences has developed a machine that can sequence single molecules of DNA and, thereby, reduce the time and cost of sequencing an individual's genome.

The effectiveness of the single-molecule DNA sequencers lies in the fact that they do not require the DNA to be 'amplified'-i.e. copied into multiple, identical strands-before it is sequenced.

The amplification step can introduce errors into the sequence and does not work well for some DNA fragments, making it difficult to sequence a genome's full complement of DNA.

"They're cool. Eventually, single-molecule sequencing will be what we use," Nature magazine quoted Edward Rubin, director of the US Department of Energy's Joint Genome Institute-a genome-sequencing facility in California-as saying.

Helicos' technique is based on a method called 'sequencing by synthesis', which begins by chopping the genome into small fragments.

An enzyme then attaches a short DNA tag onto the end of each fragment. The tag binds to a complementary DNA molecule attached to a platform, anchoring the DNA fragment in place.

A DNA replicating enzyme is then added along with a stock of DNA 'letters' or bases carrying fluorescent labels. As the fluorescent DNA forms into strands that complement the genome fragments, a camera takes a picture of each newly added base.

So far, Helicos has used its machine to sequence the genome of a virus called M13 that infects bacteria, which is nearly a millionth the size of the human genome.

Experts at the firm reckon that their machine may be ready to sequence a human genome for about 72,000 dollars in eight weeks.

The firm's official web site says that the machine itself will cost customers about 1.35 million dollars.

ANI

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