Changes in the phosphorylation of non-histone chromatin proteins during the cell cycle of HeLa S3 cells

Abstract

The phosphorylation of non-histone chromatin proteins in synchronized HeLa S3 cells was studied in 5 phases of the cell cycle: mitosis, G1, early and late S, and G2. The rate of non-histone chromatin protein phosphorylation was found to be maximal during G1 and G2, somewhat decreased during S phase, and almost 90% depressed during mitosis. Analysis of the phosphorylated non-histone chromatin proteins by SDS-acrylamide gel electrophoresis showed a heterogeneous pattern of phosphorylation as measured by labeling with 32P. Significant variations in the labeling pattern were seen during different stages of the cell cycle, and particular unique species appeared to be phosphorylated selectively during certain stages of the cycle.