Characterization of Two CHO Variants in Respect to MNNG-Induced Cell Killing, Mutations, and Repair of Methylated DNA Bases
Two Chinese hamster ovary (CHO) cell variants differ substantially in their sensitivity to N-methyl-N’ -nitro-N-nitrosoguanidine (MNNG). The resistant clone (Cl 3) was isolated from the sensitive parent line (Cl 9) after treating Cl 9 cells with a highly cytotoxic dose of MNNG. In contrast to their different sensitivity to the toxic effect of MNNG, the two variants are equally sensitive to its mutagenic effect. MNNG methylates DNA of Cl 9 and Cl 3 to the same extent. Loss of the two methylated purines N3-methyladenine and N7-methylguanine from DNA occurs at the same rate. O6 -methylguanine is not repaired in either clone. We conclude that the increased resistance of Cl 3 is neither due to a reduced uptake or binding of MNNG, nor due to an increased repair of the major methylated bases in DNA.
KeywordsHydrolysis Ethyl Penicillin Streptomycin Methylenechloride
Unable to display preview. Download preview PDF.