Immunoelectron microscopical distribution of poly(ADP-ribose)polymerase in the mammalian cell nucleus

The ultrastructural distribution of poly(ADP-ribose)polymerase has been studied using a specific antibody and immunocytochemistry with immunogold markers. In situ localization in synchronized Chinese hamster ovary cells reveals the antibody associated with mitotic chromosomes, and later with condensed chromatin and perichromatin regions in G1 phase. During S and G2, the label occurs mostly on perichromatin regions where perichromatin fibrils are also observed. In the nucleolus, the label appears especially on the dense fibrillar component and to a minor extent on the granular component. Immunolabeled spread active chromatin preparations from exponentially growing cultured mouse P815 cells indicate preferential association of the antibody with nascent nonribosomal RNP fibrils compared to inactive chromatin. The results, suggesting a relationship between the poly(ADP-ribose)polymerase occurrence and RNA (or RNP) formation, are discussed in view of the present knowledge about possible relations between poly(ADP-ribosylation) and synthesis of RNA and DNA.