Use of denaturing-gradient gel electrophoresis to study chromium-induced point mutations in human cells.

A large number of hprt-mutants were obtained by treating human lymphoblast cells (TK6) with 5 microM K2Cr2O7 for 5 hr and selecting by growth in 6-thioguanine. A combination of high fidelity polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) allowed us to measure mutant frequencies as a function of DNA sequence. Chromium(VI) induced four hotspots in a 104 bp domain of hprt exon 3. Substitutions at G:C base pairs were the predominant mutations. One of the chromium-induced hotspots was located at the same position as previously determined hydrogen peroxide and benzo(a)pyrene diol epoxide hotspots.