Production of high levels of phosphorylated F1 histone by zinc chloride.

Methods have been sought to perturb the level of phosphohistones. ZnCl2 (10 mM) exhibits histone phosphate phosphatase in vivo in HTC cells and leads to hyperphysiological levels of F1 phosphohistone. Treatment of tissue culture cells with this concentration of ZnCl2 leads to a reduction in medium pH to 6.4. Control experiments have indicated that HTC cells grow efficiently at this pH and that the reduction of pH does not produce the hyperphosphorylated state per se. The optimum conditions for the ZnCl2 effect are described. That the effect of ZnCl2 on the heterogeneity of F1 histone is due to an effect on phosphorylation was demonstrated by the observation that the entire effect is abolished by treatment with alkaline phosphatase. The site of phosphorylation is in the carboxy-terminal end of the F1 molecule. The inhibitory effect of ZnCl2 on F3 phosphorylation in metaphase cells is also described.