DNA-interacting proteins in the spermiogenesis of the mollusc Murex brandaris

Sperm chromatin of Murex brandaris (a neogastropod mollusc) undergoes a ser ies of structural transitions during spermiogenesis. The DNA-interacting pr oteins responsible for these changes as well as the mature protamines prese nt in the ripe sperm nucleus have been characterized. The results reveal th at spermiogenic nuclear proteins are protamine precursors that are subjecte d to a substantial number of small N-terminal deletions that gradually modi fy their overall charge. The composition of mature protamines is remarkably simple in turn, promoting an efficient and extremely tight packaging of DN A. The pattern of spermiogenic chromatin condensation in IM. brandaris clea rly departs from that corresponding to vertebrate chromatin.