Intracellular distribution of poly(ADP-ribose) synthetase in rat spermatogenic cells

The highest activity of poly(ADP-ribose) synthetase was found in the testis among several rat tissues tested. Subcellular fractionation of the testis demonstrated that the synthetase was localized primarily in the nucleus and partially in the microsomal-ribosomal fraction. This result was confirmed by immunocytochemical staining with the enzyme-specific antibody. The synthetase was localized in the nuclei of interstitial cells, Sertoli cells, spermatogonia, and spermatocytes. In addition, round spermatids showed a granular staining in the cytoplasm, which was comparable in intensity with that in the nucleus. The cytoplasmic synthetase had a molecular weight of 115,000 and synthesized oligomers of ADP-ribose on itself (automodification). The synthetase activity in the isolated cytoplasmic fraction was stimulated about threefold by the addition of DNA and depressed by treatment with DNase I, suggesting the presence of endogenous activator DNA. A candidate DNA for such an activator was isolated from the microsomal-ribosomal fraction, and identified tentatively as mitochondrial DNA on the basis of its size and restriction fragment patterns.