Self-association of Chaetopterus variopedatus sperm histone H1-like. Relevance of arginine content and possible physiological role.

Self-association of histones H1 from calf thymus and from sperm of the marine worm Chaetopterus variopedatus was studied on native and glutaraldehyde cross-linked molecules by PAGE and by salt-induced turbidity measurements. Multiple polymers were generated by native sperm histone H1-like after glutaraldehyde cross-linking while the same treatment on its lysine- or arginine-modified derivatives and on somatic histone H1 failed to induce polymerization. This result suggests the relevance of arginine content in the formation of histone H1-like polymers particularly because Chaetopterus variopedatus and calf thymus histones H1 have similar content of lysine but different K/R ratio (2 and 15, respectively). Salt-induced turbidity experiments confirmed the high tendency of sperm histone H1-like to form oligomers, particularly in the presence of phosphate ions. Native PAGE analysis in the presence of phosphate supported this hypothesis. The reported results suggest that phosphate ions connecting lysine and arginine side chain groups contribute to the interaction of sperm histone H1-like with DNA in chromatin and play a key role in organization and stabilization of the chromatin higher order structures.