[Evolutionary interrelationship of histones H1 and H5 in vertebrates]

Lysine-rich histones of some amphibians and fishes were studied. Electrophoretically purified subfractions were cleaved at residues of tyrosine, methionine, aspartic acid and phenylalanine. The fragments thus obtained were investigated by the method of incomplete succinylation which permitted us to determine the number of lysine residues, positive charge in acid conditions and molecular lengths of polypeptides. It was found that in anura and shark the fraction H1a resembled the histone 5 of birds in its N-terminal half part of the molecule. However this fraction proved to be non-tissue-specific. Other histone 1 fractions characteristic for vertebrates were represented in the present study by molecular variant H1s which was different from H1a fraction by the number and position of tyrosine, methionine and aspartic acid residues. The erythrocyte-specific fraction of the lysine rich histone was found in the following families of fishes: Salmonidae, Percidae and Cyprinidae. A high degree of homology in the structure of N-terminal half of H1s and histone 5 of fishes has been observed. On the basis of these results we propose a hypothesis of the independent origin of the avian and fish H5 from different fractions of H1.