Field gradients improve resolution on DNA sequencing gels.

A simple field gradient technique which leads to sharpening of bands and to an increase in the number of resolvable bases per gel is described. About 300 bases per sample application could be resolved on a 53-cm-long field gradient 6% gel, compared with about 200 on a standard gel. Gels of increasing cross-sectional area, producing the field gradients, are prepared by varying the thickness of spacers along the gel. Compared with the ionic strength gradient method, the field gradient method described here uses the standard sliding technique for preparation of very thin gels and does not require any special skills or preparation of more than one gel solution. Other possible gradient techniques are discussed.