Phosphorylation of nonhistone chromosomal proteins early during the prereplicative phase of the cell cycle of WI-38 human diploid fibroblasts.

Stimulation of confluent monolayers of nondividing WI-38 cells to proliferate is accompanied by a doubling in the rate of phosphorylation of nonhistone chromosomal proteins during the first hour. The use of cycloheximide to inhibit protein synthesis does not appear to affect phosphorylation of the nonhistones. Nondividing and serum-stimulated cells exhibit qualitative differences in the phosphorylation and dephosphorylation of individual polypeptide peaks resolved by polyacrylamide gel electrophoresis. These results are consistent with other evidence implicating nonhistone protein phosphorylation as an early event involved in the activation of transcription occurring during cell proliferation.