Evidence for nonhistone chromosomal protein kinase activity associated with nucleosomes isolated from HeLa S 3 cells

Abstract

Nonhistone chromosomal proteins and phosphorylation of chromosomal polypeptides have been implicated in the structural and transcriptional properties of the eukaryotic genome [l-6]. However, the relationship between phosphorylated nonhistone chromosomal proteins and the basic structural units of the eukaryotic genome, nucleosomes, remains to date an open-ended question. In an attempt to address the biological significance of nonhistone chromosomal protein phosphorylation, we have examined the representation of phosphorylated nonhistone chromosomal proteins-and protein kinase activity in nucleosome cores isolated from exponentially growing HeLa S3 cells. Evidence is presented which suggests that HeLa cell nucleosome preparations contain protein kinase activity that phosphorylates nonhistone chromosomal proteins but exhibits little ability to phosphorylate core histones. This protein kinase activity decreases with increasing nucleosome oligomer chain lengths; however, nuclease cleavage of oligomers to monosomes results in an increased level of protein kinase activity.