LEAD ACETATE MUTAGENICITY AND MUTATIONAL SPECTRUM IN THE HYPOXANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE GENE OF CHINESE-HAMSTER OVARY K1 CELLS

The molecular nature of lead-induced mutations was examined in this st udy to more thoroughly understand lead mutagenesis. Chinese hamster ov ary K1 cells were exposed to 0.5-3 mM lead acetate for 24 h. The media n lethal dose (LD(50)) value was 1.5 mM, and the hypoxanthine guanine phosphoribosyltransferase (HPRT) mutant frequency increased linearly a s lead concentrations were raised from 0.5 to 1.5 mM. We also amplifie d the HPRT cDNAs of 56 independent lead-induced mutants by reverse tra nscriptase-polymerase chain reaction (PCR). Forty-two mutant cDNAs wer e successfully amplified: 36 mutants had transcripts of normal or slig htly smaller than normal size, and six mutants had large deletions. Th e other 14 mutants whose HPRT cDNA could not be amplified were subject ed to genomic-DNA PCR analysis. All of those mutants had one or more e xons missing from their genomic HPRT DNA. DNA sequencing of mutant cDN As showed that 22 had single-base substitutions, four had small altera tions, 10 had single-exon deletions, and six were missing two or three exons. Furthermore, DNA sequencing of the HPRT intron-exon boundaries in eight splice mutants revealed that all of them had single-base sub stitutions in their genomic DNA. G . C base substitutions occurred 3.3 -fold more frequently than AT base substitutions. Similar frequencies were observed for G . C --> A . T, G . C --> T . A, and G . C --> C . G mutations. These results suggest that G . C base pairs may be the pr imary target sites for lead mutagenesis. (C) 1996 Wiley-Liss, Inc.