Phosphorylation of H1 subtypes in regenerating rat liver.

H1 histone of rat liver consists of four molecular species designated as H1-1, -2, -3, -4. After partial hepatectomy, phosphorylation of H1-3 was induced first, occurring even within 15 h after the operation. By partial hepatectomy, the rate of incorporation of [3H]lysine into H1 histone increased an average of 4-5 times, but that into H1-4 increased 16-20 times. This actively synthesized H1-4 was subsequently degraded rapidly. Thus induction of this active turnover of H1-4 seems to be correlated with liver regeneration. The maximum activity for phosphorylation of H1-3 attained in regenerating liver was five times that in normal liver. By 36 h after the operation, the phosphorylated peak in the chromatographic pattern had moved forward to a position between the peaks of H1-2 and H1-3, named H1-3'. The newly synthesized H1-3 was not transferred appreciably to H1-3' within 30 h after the operation. At 48 h after the operation, H1-3' amounted to 40% of the total H1-3 subtype. The specificity of the phosphorylation reaction was examined in a reaction system consisting of isolated H1 histone and cAMP-dependent kinase. It was concluded that the specificity of the phosphorylation reaction in vivo was due mainly to the difference in structures of different H1 subtypes.