ADP-ribosylation of core histones was investigated in isolated nuclei of Physarum polycephalum. Core histone species differed in the mode of modification. Whereas ADP-ribosylation of H2A and H2B is sensitive to inhibition by 3-methoxybenzamide, as with most other nuclear acceptor proteins, the modification of H3 and H4 is not inhibited. Cleavage experiments with hydroxylamine indicate a carboxylate ester type ADP-ribose-protein bond for H2A and H2B and arginine-linked ADP-ribose residues for H3 and H4. ADP-ribosylation preferentially occurs on acetylated histone subspecies, as shown for H4. These data are substantiated by the use of n-butyrate, which induces hyperacetylation of core histones; the butyrate-induced shift towards more acetylated H4 subspecies is accompanied by an increase of ADP-ribose incorporation into highly acetylated H4 subspecies.

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