Abstract
A 63 kDa protein is detectable in the culture fluid of mouse BALB/c‐3T3 cells traversing from the G0, state to the G1 phase, whereas it is undetectable in the culture fluid of quiescent or growing BALB/c‐3T3 cells. Secretion of the protein is maximal at 10 h after serum addition. G0‐specific ts mutant cells (rat tsJT60) also secrete the 63 kDa protein only when the quiescent cells are stimulated by serum addition at permissive temperature. These facts indicate that the 63 kDa protein is secreted only from cells traversing from the G0, state to the G1, phase.