ISOLATION OF A TEMPERATURE-SENSITIVE CELL CYCLE VARIANT OF CHINESE HAMSTER CELLS

Abstract

A temperature-sensitive cell cycle variant, ts-1 has been isolated from a pseudodiploid Chinese hamster cell line, D6 after mutagenesis with EMS and cytosine arabinoside selection. The ts-1 grows well at the permissive temperature, 34°C, but not at the non-permissive temperature, 40°C, although some fractions of the cells divide once when shift up the temperature to 40°C. The ts-1 was further examined by autoradiography to determine if any functions at a unique stage in the cell cycle is defective at the non-permissive temperature. The studies on the rates of macromolecular synthesis revealed that the overall rate of DNA synthesis, but not RNA and protein synthesis, was affected at the non-permissive temperature. The cessation of DNA synthesis was mainly due to a decrease in the number of cells synthesizing DNA. These results together with studies on asynchronous and mitotically synchronized cells suggest that the ts-1 is a cell cycle variant defective in a function which is active throughout the entire G1 phase and is required for entry to the S phase, but no longer required once cells enter the S phase.