Helicos BioSciences, a Cambridge, Massachusetts company, has just published a report in the latest Science that demonstrates the ability to sequence a complete genome of an organism (M13 virus in this case) by analyzing a single molecule of DNA without amplification. We have initially covered Helicos’ technology back in April, 2005.
The company reports:
The report demonstrates that the tSMS technology can reliably re-sequence a moderately complex genome without the associated errors, cost, and experimental complexity of amplification. The tSMS process captures images of single dye labeled nucleotides as they are incorporated to determine the sequence of the individual DNA strands. In addition, the tSMS method simplifies the DNA sample preparation process and maximizes throughput by packing individual strands of DNA at high densities onto the sequencing surface.
A look at Helicos’ True Single Molecule Sequencing(tSMS)™ technology:
tSMS enables the simultaneous sequencing of large numbers of strands of single DNA or RNA molecules by using a proprietary form of sequencing-by-synthesis in which labeled DNA bases are sequentially added to the nucleic acid templates captured on a flow cell. Our optimized formulation ensures high accuracy of each base addition, which are detected by the HeliScope™ Single Molecule Sequencer to elucidate the sequence of bound strands.
How tSMS Works
Within two flow cells, billions of single molecules of sample DNA are captured on an application-specific proprietary surface. These captured strands serve as templates for the sequencing-by-synthesis process:
Polymerase and one fluorescently labeled nucleotide (C, G, A or T) are added.
The polymerase catalyzes the sequence-specific incorporation of fluorescent nucleotides into nascent complementary strands on all the templates. After a wash step, which removes all free nucleotides, the incorporated nucleotides are imaged and their positions recorded. The fluorescent group is removed in a highly efficient cleavage process, leaving behind the incorporated nucleotide. The process continues through each of the other three bases. Multiple four-base cycles result in complementary strands greater than 25 bases in length synthesized on billions of templates—providing a greater than 25-base read from each of those individual templates.
Product page: Helicos’ True Single Molecule Sequencing(tSMS)™ technology…
Abstract: Single-Molecule DNA Sequencing of a Viral Genome Science 4 April 2008: Vol. 320. no. 5872, pp. 106 – 109
Press release: Helicos BioSciences Announces Single Molecule DNA Sequence Data Published in Science Magazine…