Histone phosphorylation in synchronized mammalian cell cultures

Abstract

Synchronized cultures of mammalian cells were labeled with inorganic radiophosphorus ( 32P). Incorporation of label into histone fractions as alkali-labile 32P-phosphate was followed through the cell cycle from late G 1, through S and G 2, into early M. No evidence was obtained for the incorporation of phosphorus into histone fractions F2a or F3. The phosphorus content of histone fraction F1 rose steadily during this period, with no evidence of dephosphorylation, while the phosphorus content of histone fraction F2b rose to a maximal value in mid-S and declined rapidly thereafter. Evidence is presented for differential phosphorylation and dephosphorylation of specific histone fractions. The significance of these observations is discussed.