The relationship between molecular and cellular repair from potentially lethal damage induced by N-methyl-N'-nitro-N-nitrosoguanidine in Chinese hamster V79 cells.

The relationship between molecular and cellular repair from potentially lethal damage (PLD) induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was investigated in exponentially growing V79 Chinese hamster cells. We compared the repair processes by an alkaline sucrose sedimentation analysis and a colony formation assay. MNNG-treated cells were exposed to the conditioned medium (CM) from density-inhibited plateau-phase V79 cell cultures, as a post-treatment for the induction of PLD repair. When MNNG-treated cells were postincubated in CM, cell survival continuously increased for 18 h, and during this period, DNA replication was substantially suppressed. CM did not inhibit the rejoining of the single-strand breaks of parental DNA. Rather, parental DNA fragments sedimented more rapidly when postincubated in CM than in fresh medium. These data indicate that cellular recovery from MNNG-induced PLD increases in proportion to the resealing of MNNG-induced single-strand breaks of DNA during the suppression of DNA replication, suggesting that excision repair is involved in the PLD repair process.