The analysis of the poly(ADPR) polymerase mode of action in rat testis nuclear fractions defines a specific poly(ADP-ribosyl)ation system associated with the nuclear matrix.

The poly(ADP-ribosyl)ation system, associated with different nuclear fractions of rat testis, has been analyzed for both pADPR and pADPR acceptor proteins. The DNase I sensitive and resistant chromatin contain 35% and 40%, respectively, of the total pADPR synthesized in intact nuclei incubated with [32P]NAD. Moreover, the residual 25% were estimated to be associated with the nuclear matrix. Three different classes of pADPR are present in the nuclei. The longest and branched ADPribose polymers modify proteins present in the DNase I resistant (2 M NaCl extractable) chromatin and in the nuclear matrix, whereas polymers of> 20 residues interact with the components of the DNase I sensitive chromatin and oligomers of 6 ADPribose residues are bound specifically to the acid-soluble chromosomal proteins, present in isolated nuclear matrix. The main pADPR acceptor protein in all the nuclear fractions is represented by the PARP itself (auto-modification reaction). The hetero-modification reaction occurs mostly on histone H1 and core histones, that have been found associated to DNase I sensitive and resistant chromatin, respectively. Moreover, an oligo(ADP-ribosyl)ation occurs on core histones tightly-bound to the matrix associated regions (MARs) of chromatin loops.