ADP-ribosylation of histone H1. Identification of glutamic acid residues 2, 14, and the COOH-terminal lysine residue as modification sites.

In vitro ADP-ribosylation sites of rat liver histone H1 were determined.ADP-["Clribosyl histone H1 (average chain length = 1.1) was prepared by incubation of chromatin with 1 m~ [diose(NiWV)-"C]NAD and extracted with 5% HClO.. Bisection of histone H1 with Nbromosuccinimide demonstrated that both the N H 2and COOH-terminal halves were modified.The chemical stabilities of the bonds between ADP-ribose and both of the bisected peptides were almost identical; the bonds were stable in 0.1 M HCI, but labile in 0.1 M NaOH and 2 M NHzOH (pH 7.0).Digestion of the bisected fragments with various proteases and snake venom phosphodiesterase yielded three peptides associated with ['4C]ribose 6-phosphate.These peptides had the amino acid sequences (N-blocked)-Ser-Glu-Thr, Ala-Pro-Ala-Glu-Lys, and Ala-Lys-Lys-Lys; the former two were obtained from the NHa-terminal half in yields of 6.0 and 2.3%, respectively, while the last was obtained from the COOH-terminal half in a yield of 6.0%.By comparison with known sequences of rabbit thymus and other histone Hl's these peptides were assigned to