Biology of the histones

The biological roles of the histones are multiple; by complexing to DNA they cause such DNA to be inactive as a template for RNA polymerase; they cause supercoiling of the DNA which would appear to be a fundamental requirement for further orders of supercoiling, presumable exemplified by metaphase chromosomes; a particular histone even forms interpolypeptide disulfide bridges during metaphase, apparently stabilizing the chromosomes in a highly condensed state. It is no doubt because of this multiplicity of functions that the primary structure of the individual histone species has been conserved to an extraordinary degree since the time of the common ancestor of the higher eukaryotes.