WHY CAN WE NOT SEQUENCE THOUSANDS OF DNA BASES ON A POLYACRYLAMIDE-GEL

Pulsed fields have been remarkably useful at extending the range of DNA molecular sizes that can be separated on agarose gels by controlling the field-induced molecular orientation that often limits the resolution of large molecules. Unfortunately, the same approach seems to be much less effective for DNA sequencing on polyacrylamide gels. We present an experimental and theoretical (modelling) study of DNA sequencing which shows that molecular orientation is indeed not the main limiting factor for sequencing devices that use moderate field intensities and polyacrylamide as a separating matrix. We examine the interplay between electric field intensity, molecular size and resolution, and we suggest different approaches to increase the resolution limit of standard and automated sequencing gels. The theoretical limits of high-field electrophoretic sequencing are also discussed. We conclude that new ideas will be needed to go beyond one kilobase.