Karyotype abnormalities in a variant Chinese hamster cell line resistant to methyl methanesulphonate

A variant cell population, isolated from V79-C13 Chinese hamster cells after two consecutive treatments with methyl methanesulphonate (MMS), was found to be highly resistant to killing by this alkylating agent. The resistant cell line was cytogenetically characterized both by the presence of a stable translocation involving metacentric chromosome 2 and acrocentric chromosome 6 and by a supernumerary chromosome originated by the duplication of a small telocentric chromosome. This cell population also showed a transient transformed phenotype, seen as formation of transformed foci containing cells with high chromosomes counts and multiple chromosomal aberrations. As MMS-resistance and karyotype changes are permanent and heritable traits, we suppose that they are related events.