Dephosphorylation of histone fractions of cultured mammalian cells

Abstract

The dephosphorylation rates of labeled histone phosphate groups were determined in both random and synchronized mammalian cell cultures. In random cultures with doubling times of 16 hr, the half-lives of the phosphate contents of histone fractions F1 and F2b were found to be 7 and 13 hr, respectively. In synchronized cultures, little or no phosphate turnover was observed in G 1 for either fraction. The phosphate-specific activities of both fractions dropped to approximately half their G 1 values during S, presumably as a result of the biosynthesis of histone during this period. Dephosphorylation of histone F 1 continued at a reduced rate during G 2-M, while dephosphorylation of histone F2b ceased during this period. The relationship of these observations to postulated biological roles for histones is discussed.