Protein synthesis and the presence or absence of a measurable G1 in cultured chinese hamster cells

V79-8 cells lack a measurable G1 interval under normal growth conditions. We found that partial inhibition of protein synthesis using low levels of cycloheximide (0.05 mu/ml) could induce a measurable G1 in these cells without any significant effects on S, G2, or M. In view of these findings, recessive mutants selected from the V79-8 cell line, which each express G1, were analyzed for their rates of protein synthesis and degradation/loss. Three of the four mutants showed a decreased rate of protein synthesis sufficient to account for their G1 lengths. A fourth mutant, however, showed parental rates of both protein synthesis and degradation/loss. These results suggest not only that a G1 interval can be expressed as a result of a decreased rate of protein synthesis, but that other alterations (mutations) other than those simply affecting overall protein synthesis can result in the expression of a measureable G1 interval.