Mutational spectrum of chromium(VI) in human cells.

The mutational spectrum of K2Cr2O7 on the low melting domain within exon 3 of hypoxanthine guanine phosphoribosyl transferase (hprt) gene was obtained from 6-thioguanine-resistant (6TGr) human lymphoblasts (TK6). Using a combination of high-fidelity polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE), we found four chromium(VI) induced hotspots in a 104-bp target sequence. The hotspots were C:G-->A:T at bp 243, representing 4.5% of 6TGr mutants; A:T-->T:A at bp 247 (2.0%); G:C-->A:T at bp 289 (2.5%) and C:G-->T:A at bp 312 (4.0%). Mutational hotspots at bp 243 have previously been determined for hydrogen peroxide (C:G-->G:C) and benzo[a]pyrene diol epoxide (C:G-->A:T). Two of the hotspots, bp 243 and 289, arose in a common quadruplet 5'-ACAT-3' in the untranscribed and transcribed strands respectively.