Phosphorylation of non-histone proteins in the regulation of chromosome structure and function

Non-histone chromosomal proteins are phosphorylated and dephosphorylated within the intact nucleus by two independent sets of reactions, a protein kinase reaction which transfers the terminal phosphate group of a variety of nucleoside and deoxynucleoside triphosphates to serine and threonine residues in the proteins, and a phosphatase reaction which cleaves these phosphoserine and phosphothreonine bonds and releases inorganic phosphate. Several lines of evidence are consistent with the hypothesis that the phosphorylation and dephosphorylation of these proteins is involved in gene control mechanisms, including the findings that phosphorylated non-histone proteins are highly heterogeneous and their phosphorylation patterns are tissue specific, changes in their phosphorylation correlate with changes in chromatin structure and gene acticity, addition of phosphorylated non-histone proteins increases RNA synthesis in vitro. and phosphorylated non-histone proteins bind specifically to DNA. Cyclic AMP has both stimulatory and inhibitory properties on non-histone protein phosphorylation, depending on the enzyme fraction and substrate employed A specific protein component whose phosphorylation is inhibited by cyclic AMP has been found to be associated with RNA polymerase. The cyclic AMP-induced decrease in the phosphorylation of this protein correlates with an enhancement of RNA synthesis in vitro. These results suggest that both phosphorylation and dephosphorylation of chromatin-associated proteins may be involved in the control of gene readout.