Non histone chromosomal proteins. Evidence for their role in mediating the binding of histones to deoxyribonucleic acid during the cell cycle

Abstract

By selective dissociation of histones with the ionic detergent sodium deoxycholate, it is demonstrated that these basic chromosomal polypeptides, which are effective inhibitors of transcription, are more tenaciously bound to DNA in mitotic than in S phase chromatin. Evidence is presented which suggests that cell cycle stage specific nonhistone chromosomal proteins can account for such variations in the association of histones with DNA. When chromatin is reconstituted with DNA and histones are pooled from S phase and mitotic cells and either S phase or mitotic nonhistone chromosomal proteins, a preferential extraction of histones with sodium deoxycholate from chromatin reconstituted with S phase rather than mitotic nonhistone chromosomal proteins is observed. In contrast, the extractability of histones with sodium deoxycholate from nucleohistone complexes reconstituted with DNA pooled from S phase and mitotic cells and either S phase or mitotic histones is identical. Since nonhistone chromosomal proteins rather than histones are responsible for the differences in chromatin template activity during S phase and mitosis, it is proposed that nonhistone chromosomal proteins may modify gene expression during the cell cycle by mediating the binding of histones to DNA.