The poly(ADP-ribosylation) of chromosomal proteins is an epigenetic consequence of clastogenic DNA damaging agents which affects chromatin structure and function. We studied the poly(ADP-ribosylation) of the major classes of histones in response to DNA breakage induced by an extracellular burst of active oxygen (AO) or the alkylating agent N-methyl-N'-nitrosoguandine (MNNG) in the immortalized human keratinocytes HaCa T using a combination of affinity chromatography on phenylboronate resin and immunoblotting with polyclonal antibodies against histones H1, H2B, H2A, H3, and H4. The following findings characterized the poly(ADPR) reaction: (1) pretreatment of nuclear extracts with snake venom phosphodiesterase which removes poly(ADPR) chains strongly reduced the material which was retained by phenylboronate; (2) the ADPR transferase inhibitor benzamide (100 microM) suppressed AO-induced poly(ADP-ribosylation); (3) poly(ADP-ribosylation) reduced the electrophoretic mobility of the modified histones. Several histones were constitutively poly(ADP-ribosylated) in untreated controls: 0. 03% of H2A, 0. 04-0. 06% of H2B, and 0. 04% of H3. 1 carried at least one poly(ADPR) chain of undetermined length. AO transiently increased the poly(ADPR) levels of all major histones with the exception of H1. The extent of substitution 30 min after exposure to AO generated by 50 micrograms/mL xanthine and 5 micrograms/mL xanthine oxidase was 0. 8% for A24 greater than 0. 3% for H4 greater than 0. 1% for H3. 1 = 0 VSports手机版. 1% for H3. 2 = 0. 1% for H2B. 2 greater than 0. 09% for H2A. Within 60 min, poly(ADPR) substitution had decreased to control levels for H3 and H4 and below control levels for H2A and H2B. (ABSTRACT TRUNCATED AT 250 WORDS) .