Role of Histones in Chromatin Condensation

Abstract

We have attempted to discover which of the proteins of hen erythrocyte chromatin maintain it in the condensed state at physiological concentrations of cations. After removal of histones F2C and F1 from the chromatin there was a change in its sedimentation properties over a range of cation concentrations, and it now resembled an “uncondensed” fraction from rat liver chromatin. Removal of larger quantities of other histones (F2a2, F2b and part of F2al and F3) did not produce this change. On removal of histones F1, F2a2, F2b and F2c condensation of the chromatin was lost. Condensation was regained on reassociation with all the histones removed, or with F1 or F2c, but not with F2a2 plus F2b in similar quantities. Thus histones F2c (peculiar to nucleated erythrocytes) and F1 appear to be primarily responsible for maintaining hen erythrocyte chromatin in a condensed state. We conclude that in the genetically active uncondensed fraction of rat liver chromatin the condensing effect of F1 histones is antagonised by additional negatively charged molecules.