Isolation of a G0-specific ts mutant from a Fischer rat cell line, 3Y1.

A ts mutant clone, tsJT60, was isolated from Fisher rat cell line, 3Y1. During the exponential growth at both 34 and 39.5 degrees C, tsJT60 did not appear as ts mutant cells. However, once entered resting state (G0) under serum deprivation at the confluent state, they could re-enter S phase at 34 degrees C but could not at 39.5 degrees C following the stimulation of cells either by the addition of fetal bovine serum or by trypsinization and replating. These and other results suggested that tsJT60 is a G0-specific ts mutant, i.e., the cells have ts defect(s) in the function which is required for the stimulation from the resting state to S phase but not for the progression of the cell cycle in an exponential growth phase.