Nuclear matrix-associated poly(ADPribosyl)ation system in rat testis chromatin

The presence of poly(ADPR)polymerase in the third level of rat testis chromatin, i.e., in stripped chromatin loops and nuclear matrix, was assessed using enzymatic assays, activity blots, and Western blots. The distribution and the size of ADPribose polymers associated to proteins of the same nuclear fractions was analyzed after incubation of intact isolated nuclei with [14C]- or [32P]NAD+. Short ADPribose oligomers, not larger than 3 residues, were found to be associated to tightly bound chromosomal proteins, which resisted extraction by 2 M NaCl, whereas longer oligomers (8-13 residues long) were associated to loosely bound chromosomal proteins. The identity of ADPribose-protein conjugates was determined by autoradiographic analysis of nuclear protein extracts. Tightly bound histone-like proteins appear to be ADPribosylated both in stripped chromatin loops and in nuclear matrix.