STRAND-SPECIFIC MUTATION-INDUCTION BY 1,2-DIBROMOMETHANE AT THE HYPOXANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE LOCUS OF CHINESE-HAMSTER OVARY CELLS

The nature of mutations induced by 1,2-dibromoethane (DBE) at the hprt (hypoxanthine-guanine phosphoribosyltransferase) gene was analysed in Chinese hamster ovary (CHO-9) cells. Molecular characterization of 36 hprt mutants at the cDNA level yielded 19 GC-->AT transitions, two AT -->CG transversions, three frameshift mutations, two identical small d eletions and 10 exon deletions, Further analysis of the deletion mutan ts by amplification of specific exons from genomic DNA showed two more GC-->AT transitions at splice sites and an similar to 70 bp deletion, Assuming that the S-[2-(N7-guanyl)ethyl]glutathione adduct is respons ible for the GC-->AT transitions, 90% of the affected guanines were lo cated in the non-transcribed strand of the hprt gene, suggesting a str and bias in repair of this adduct, Nearest neighbour analysis of induc ed GC-->AT transitions indicates a preference for a 5'-PyPu (G) under bar DNA sequence, i.e. 15/21 mutated guanines were located in either a TG (G) under bar or a CA (G) under bar DNA sequence, These molecular data on DBE-induced mutations showed similar features as data from a s tudy by Graves et al, (Mutagenesis, 11, 229-233, 1996) in which they a nalyzed 13 hprt mutants induced by DBE in CHO-K1 cells, Six of the sev en GC-->AT mutations were on positions mutated more than once among th e 36 hprt mutants in the present study, The combined findings suggest that some positions seem to be hot spots for DBE-induced mutations, Co ncerning the relevance of these in vitro studies for germ cell mutagen esis the conclusion may be that these data lend further support to the view that mutation spectra derived from in vitro systems have little predictive value for the nature of mutations induced in post-meiotic g erm cells in vivo, as demonstrated for other alkylating agents in both Drosophila and mice.