A temperature-sensitive DNA synthesis mutant isolated from the Chinese hamster ovary cell line.

A temperature-sensitive DNA synthesis mutant, tsC8, was isolated from mutagenized Chinese hamster ovary cells by the fluorodeoxyuridine suicide technique. The tsC8 cells showed inhibition of DNA synthesis at the nonpermissive temperature (NPT) with little effect on initial levels of RNA and protein synthesis. Temperature-arrested tsC8 cells had G1 or S DNA content and the temperature-sensitive (ts) period of the tsC8 cell cycle was the interval between the G1/S border and the middle of the S period. The tsC8 cells were unable to enter the S phase when exposed to the NPT during the G1 period of the cell cycle. When S phase tsC8 cells were shifted to the NPT, they incorporated [3H]thymidine at rates similar to the parental cell type for only 2 h, indicating a ts defect in DNA synthesis. The tsC8 mutation is expressed in a recessive manner and is in a gene distinct from those affected in other DNA synthesis mammalian cell mutants.