A NEW COMPLEMENTATION GROUP OF MITOMYCIN C-HYPERSENSITIVE CHINESE-HAMSTER CELL MUTANTS THAT CLOSELY RESEMBLES THE PHENOTYPE OF FANCONI-ANEMIA CELLS

Three Mitomycin C (MMC)-hypersensitive mutants (CL-V1B, CL-V5B, and CL -V101B) were isolated from Chinese hamster V79B cells by the replica p lating technique. In comparison to the parental cell Line, CL-V1B, CL- V5B, and CL-V101B show about a 22-, 32-, and 13-fold increased sensiti vity to MMC, respectively (judged by the D-10). These mutants are also sensitive to other DNA cross-linking agents, such as 1,2,3,4-diepoxyb utane (9-, 19-, and 12-fold, respectively) and cis-diamminedichloropla tinum(II) (17-, 12-, and 6-fold, respectively). CL-V5B and CL-V101B di splay an exclusive sensitivity to DNA cross-linking agents, whereas CL -V1B also shows an increased sensitivity to monofunctional alkylating agents, such as methyl methanesulfonate (3-fold) and ethyl methanesulf onate (2-fold), and UV254nm (2-fold). Approximately 2-3-fold higher le vels of spontaneous chromosomal aberrations are found in these three m utants in comparison to wild-type V79B cells. At a MMC survival level of 80%, CL-V5B demonstrates a 16-fold higher level of MMC-induced chro mosomal damage than V79B. Despite phenotypical heterogeneity within th is group of mutants, hybrid clones derived after fusion remained MMC s ensitive, indicating that these mutants belong to the same complementa tion group. To determine whether the mutants represent a new complemen tation group among other Chinese hamster cell mutants that also displa y hypersensitivity to MMC, CL-V1B cells were fused with mutants repres enting different complementation groups i.e., irs1, irs3, irs1SF, UV20 , UV41, V-H4, and V-C8 cells. In all cases, the derived hybrids regain ed MMC sensitivity similar to wild-type cells, indicating that the CL- V1B mutant represents a new complementation group. The phenotype of CL -V1B, CL-V5B, and CL-V101B cells closely resembles the phenotype of Fa nconi anemia cells, suggesting that these hamster mutants could be def ective in a gene that is involved in this disorder.