GENE AMPLIFICATION IN CHINESE-HAMSTER DNA-REPAIR DEFICIENT MUTANTS

In order to study the possible relationship between gene amplification and DNA repair we analyzed the amplification of the CAD gene in four mutants hypersensitive to UV light (CHO43RO, CHO7PV, UV5 and UV61) iso lated in vitro from Chinese hamster cell lines (CHO-K1 and AA8). These mutants are characterized by different defects in the nucleotide exci sion repair mechanism and represent complementation groups 1, 9, 2, an d 6 respectively. To evaluate the amplification ability of each cell l ine we measured the rate of appearance of PALA resistant clones with t he Luria and Delbruck fluctuation test. Resistance to PALA is mainly d ue to amplification of the CAD gene. In the mutants CHO43RO, UV5 and C HO7PV we reproducibly found an amplification rate lower than in the pa rental cell lines (2-5 times), while in UV61 the amplification rate wa s about 4 times higher. This result indicates that each mutant is char acterized by a specific amplification ability and that the unefficient removal of UV induced DNA damage can be associated with either a high er or a lower amplification rate. However, the analysis of randomly is olated CHO-K1 clones with normal UV sensitivity has shown variability in their amplification ability, making it difficult to relate the spec ific amplification ability of the mutants to the DNA repair defect and suggesting clonal heterogeneity of the parental population.