Nucleosomal organization of a part of chromatin in mollusc sperm nuclei with a mixed basic protein composition.

The structural organization of mature sperm chromatin from three representatives of the Mytilidae family has been studied. The acid-soluble proteins in these species nuclei are primarily sperm-specific (approximately 80%) with the remainder being core histones. Previously, we have shown that the mature sperm nuclei of these molluscs are compact, dense structures formed by interaction of the spermspecific proteins with DNA (1). Here we show that: a) although the histones are minor chromatin protein fraction, they still organize a part (20-25%) of the total DNA into nucleosomes; b) one of the sperm-specific proteins, different from somatic H1 or H5 histones participates in the formation of the beaded structures.