Nuclear protein modification and chromatin substructure. 3. Relationship between poly(adenosine diphosphate) ribosylation and different functional forms of chromatin

Abstract

The relationship between poly(ADP) ribosylation of nuclear proteins and functionally different forms of chromatin from mid-S-phase HeLa [human cervical carcinoma] nuclei was investigated. Unique nonhistone proteins were apparently modified in mid-S-phase HeLa nuclei. The major acceptor for poly(ADP-ribose) [poly(ADP-Rib)] was an internucleosomal nonhistone protein (protein C; MW 125,000). Histones H3, H1, H2b and H2a but not H4 were ADP-ribosylated in S-phase nuclei. Chromatin fragments preferentially released by micrococcal nuclease were enriched in nonhistone proteins, poly(ADP)-ribosylated nuclear proteins, poly(ADP-Rib) polymerase activity and nascent DNA from the DNA replicating fork. In extended forms of chromatin, continguous to the DNA replicating fork, poly-(ADP-Rib) polymerase was maximally active. In chromatin distal to the replicating fork (i.e., more condensed structures), nucleosomal histones and histone H1 were not significantly ADP-ribosylated, and poly(ADP-Rib) polymerase activity was depressed 2- to 3-fold. A subset of nucleosomes in extended regions of chromatin is apparently subject to extensive ADP ribosylation.