New insights into protamine-like component organization in Mytilus galloprovincialis sperm chromatin

We have analyzed Mytilus galloprovincialis’ sperm chromatin which consists of three sperm nuclear basic proteins of the PL-type: PL-II, PL-III and PL-IV, in addition to a residual amount of the four core histones. The knowledge of Mytilus galloprovincialis’ sperm chromatin structure, the organization of the PL-type component in chromatin and their interactions with DNA is of considerable interest because these organisms are largely utilized as bioindicator of marine pollution that could affect its state. Our results obtained by micrococcal nuclease digestion in combination with salt fractionation suggest the existence of a likely unusual organization in which there would be a more accessible location of PL-II/PL-IV when compared to PL-III and core histones. Further we used electrophoretic mobility shift assay in order to define DNA binding mode of PLII and PLIII and turbidimetric assays to determine their self-association ability in the presence of sodium phosphate. On the base of our results we propose a model of Mytilus galloprovincialis’ sperm chromatin organization that could be useful in order to develop chromatin-based genotoxicity tests in pollution biomonitoring programs