Comparison of the histones from fish erythrocytes

Abstract

Because of contentions concerning the generality of cell-specific histone 5 (H5) in nucleated erythrocytes of species other than birds, the erythrocyte histones of carp, trout, perch, black crappie, and white sucker were studied under conditions which minimize proteolysis. All were examined by polyacrylamide gel electrophoresis, and histone 1 (H1) and H5 were purified by cation-exchange chromatography on Amberlite CG-50 and by exclusion chromatography through BioGel P60.A protein homologous to H5 could be isolated and identified from the mature erythrocytes of carp, trout, perch, and black crappie but not from white sucker. The relative amounts of H5 differed extensively and inversely in proportion to H1, implying some functional homology between these proteins. The extremely variable levels of H5, including its apparent absence from one species, suggests that typical H5 is not essential to the function or development of nucleated erythrocytes.Although H1 is the most divergent histone fraction, H5 is also highly variable. Fish erythrocyte H5 differs from avian H5 in relative electrophoretic mobility, ease of elution from Amberlite CG-50 cation-exchange columns, and amino acid composition. H5's from fish tend to have more threonine but less serine, arginine, glutamic acid, and histidine than avian H5's. Fish H5's are more diverse than avian H5's and resemble the H5 homologues from other extremely diverse species; thus avian H5 may be an extreme in specialization of an H1 subfraction.