ADP-ribosylation in vivo of
histone H1 was studied in
hepatoma cells (Yoshida AH 7974)
after treatment with the
alkylating agent dimethyl sulfate for 30 min and compared with that of other
polypeptides. In unstimulated cells,
histone H1 was only a minor acceptor (less than 4%) of total monomeric and polymeric
ADP-ribosyl residues. Induction of DNA repair by
dimethyl sulfate treatment increased total mono(
ADP-ribosyl)
protein conjugates 1.6-fold whereas
histone H1-linked mono(
ADP-ribosyl) groups were elevated greater than 30-fold, thus accounting for nearly one-fourth of the net increase in monomeric
ADP-ribosyl residues. In contrast,
histone H1-associated poly(
ADP-ribosyl) residues comprised only 2% of the total increase in
poly(ADP-ribose). The extent to which the
histone H1 population became
ADP-ribosylated was low even in
dimethyl sulfate-treated cells. Less than 2% of the
histone H1 molecules were mono(
ADP-ribosyl)ated and only 0.003% carried poly(
ADP-ribosyl) chains when an average chain length of 10 is assumed. The principal
polypeptide acceptors of alkylation-induced ADP-ribosylation were concentrated in two peaks, one migrating close to the position of core
histones H3/H2B and accepting most of the induced mono(
ADP-ribosyl) and poly(
ADP-ribosyl) residues. The other (Mr = 110,000-160,000) resembled auto-modified
poly(ADP-ribose) polymerase. Our data demonstrate marked differences of alkylation-induced (
ADP-ribosyl)n
protein patterns to analyses performed in vitro.