The electrophoretic separation of curved cisplatin-modified DNA fragments on polyacrylamide gels is dependent on the voltage gradient.

Polyacrylamide gel electrophoresis has been widely used to study DNA fragments containing sequence-dependent curvature. The anomalous electrophoretic behavior of curved DNA fragments on such gels allows their separation from straight fragments of the same length. Here we demonstrate that polyacrylamide gels can be successfully used to resolve DNA fragments modified at a single site by the antitumor drug cis-diamminedichloroplatinum(II) (cis-DDP, cisplatin) from their unmodified counterparts. However, the resolution strongly depends on the voltage gradient, being completely lost when it drops below a certain threshold level. The parameters of the electric field do not affect separation of 'normal' DNA fragments of comparable length.