Monday, October 20, 2008

The Age of Sequencing I: The Sanger Alliance

Source: Shendure and Ji (2008). Next-generation DNA sequencing. Nature Biotech 26:1135-1145.

There is no doubt that Sanger biochemistry (i.e. 'cycle sequencing') has set the fundamentals of sequencing; both in high-throughput clone based methods (e.g. shotgun) and single PCR product targeted sequenicng. In each cycle, labeled ddNTP molecules mark a single nucleotide at its end and through high-resolution electrophoretic separation, the final sequence is read. Each reaction can read about ~1000 bp, with the max accuracy of 99.999% and the cost of $0.5 per kb in shotgun.

This platform has been used for the emergence of the second generation sequencing pipelines: 454, Solexa, SOLiD, Polonator and HeliScope. These methods, despite many differences in their methodologies, follow the same 'cycling' logic followed by an optical signal of some sort. Library preparation, followed by adapter ligation and amplification is the first step of all these methods. Amplification is done either through in situ polonies, emulsion PCR or bridge PCR. The amplification step, however, should ensure the spacial clustering of each clone.

The bottom line is, these methods bypass the steps that are required in classic Sanger method and also use array-based approaches to enforce parallelism.

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