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 study to more thoroughly understand lead mutagenesis. Chinese hamster ovary K1 cells were exposed to 0.5-3 mM lead acetate for 24 h. The median lethal dose (LD50) value was 1.5 mM, and the hypoxanthine guanine phosphoribosyltransferase (HPRT) mutant frequency increased linearly as lead concentrations were raised from 0.5 to 1.5 mM. We also amplified the HPRT cDNAs of 56 independent lead-induced mutants by reverse transcriptase-polymerase chain reaction (PCR). Forty-two mutant cDNAs were successfully amplified: 36 mutants had transcripts of normal or slightly smaller than normal size, and six mutants had large deletions. The other 14 mutants whose HPRT cDNA could not be amplified were subjected to genomic-DNA PCR analysis. All of those mutants had one or more exons missing from their genomic HPRT DNA. DNA sequencing of mutant cDNAs showed that 22 had single-base substitutions, four had small alterations, 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 substitutions in their genomic DNA. G.C base substitutions occurred 3.3-fold more frequently than A.T 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 primary target sites for lead mutagenesis.
Yang
J L
JL
Department of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan, Republic of China.
Yeh
S C
SC
Chang
C Y
CY
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D006224:Cricetinae; D004252:DNA Mutational Analysis; D018076:DNA, Complementary / Q000187:drug effects / Q000235:genetics; D004351:Drug Resistance; D017353:Gene Deletion; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D007928:Lethal Dose 50; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009153:Mutagens / Q000633:toxicity*; D009942:Organometallic Compounds / Q000633:toxicity*; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D013866:Thioguanine / Q000494:pharmacology; D014158:Transcription, Genetic
D018076:DNA, Complementary; D009153:Mutagens; D009942:Organometallic Compounds; D007041:Hypoxanthine Phosphoribosyltransferase; D013866:Thioguanine; C008261:lead acetate