Critical electrolyte concentration of spermatozoal chromatin containing histone H1 variants

The critical electrolyte concentrations (CEC) of sperm chromatin from anima l species known or suspected to contain histone H1 variants were compared b y examining the affinity or their DNA-protein complexes for toluidine blue in the presence of Mg2+. Bullfrog, sea urchin, bee and bumblebee spermatozo a were studied. The CEC for Rana catesbeiana and two sea urchin species wer e similar to that of histone MS-containing chromatin from chicken erythrocy tes, thus confirming the biochemical and structural similarities of these D NA-protein complexes. The CEC for bees and the bumblebee, Bombus atratus, s howed no particular phylogenetic relationship. We concluded that the CEC of histone HI-containing sperm cell chromatin is a useful indicator of variab ility in DNA-protein complexes but is of little phylogenetic value.