Reading DNA with silicon—or via the glow of fireflies

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Many of the modern DNA sequencing techniques involve partially overlapping techniques, so our past articles have provided a nice foundation. In this case, the tethered PCR approach that we mentioned in covering SOLiD sequencing, in which beads wound up covered with multiple copies of an identical sequence, is also used by an otherwise unrelated approach, employed by Roche's 454 sequencing machines. The chemistry of the 454 sequencing reaction is radically different, and goes by the catchy name pyrosequencing.

Pyrosequencing is distinct from the rest of the techniques we'll discuss, which focus on attaching labels to the DNA bases that are added to a growing DNA strand. Instead, the pyrosequencing chemistry focuses on something that's an afterthought in most sequencing methods: the phosphate group that gets kicked off each time a DNA base is added. In our initial diagram for DNA polymerization, we showed what happens when a new triphosphate base is added to a growing DNA strand.

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