Marine invertebrate sperm-specific histones and histone-DNA interactions: circular dichroism and ultraviolet spectroscopy studies

Abstract

Circular dichroism (c.d.) and turbidity measurements have been performed to study the structural behaviour of the marine invertebrate sperm-specific histones H1, H2B and of the mollusc sperm-specific protein S2 and their dependence on ionic strength as well as the formation of complexes of these proteins with DNA. Sea urchin sperm histones H1 from Strongylocentrotus intermedius or Strongylocentrotus droebachiensis attain, at 2 m NaCl, a higher helicity than histones H1 from the sperm of the bivalve mollusc Chlamis islandicus or from calf thymus. This extra helical part of the sea urchin sperm histones H1 is rapidly digested by trypsin. The complexes of the marine invertebrate H1 and S2 proteins with DNA are characterized by c.d. spectra with strong negative ellipticities corresponding to the (-PSI)-type c.d. spectra of calf thymus H1-DNA complexes. The arginine content of the histones correlates with the ionic strength at which the formation of the protein—DNA complexes begins. The higher the arginine content the higher is the ionic strength at which complex formation sets in once ionic strength is reduced. The results of the investigations on H2B-DNA complexes point to a possible involvement of H2B from sea urchin sperm in the condensation of sea urchin sperm chromatin.