ABSTRACT
The transcription of DNA is known to be inhibited in vitro by the presence of histones. This has been shown to be true for isolated nuclei, isolated chromatin, or for DNA alone (Bonner & Huang, 1962; Bonner, Huang & Gilden, 1963; Allfrey & Mirsky, 1963 ; Allfrey, Faulkner & Mirsky, 1964; Sonnenberg & Zubay, 1965). The masking of genomic sites in adult differentiated tissues seems the most probable explanation of the expression of only a fraction of the adult genome (Paul & Gilmour, 1966). Affinities have been observed between certain base sequences in DNA and certain fractions of histones (Liau, Hnilica & Hurlbert, 1965; Skalka, Fowler, Andre & Hurwitz, 1966; Tan, 1966), yet the remarkable similarity in composition between the histones of different species and organs of the same species does not encourage the idea that histones are specific repressors of genomic function. Many authors (Zalokar, 1964; Goldberg & Atchley, 1966; Frenster 1967) have proposed hypotheses tending to reconcile the apparent non-specificity of the relation between DNA and histones and their intervention in gene function : it is thought that polyanions (RNAs, phosphoproteins, phospholipids, non-histone proteins or hormones) may remove histones from binding sites and release specific single-stranded sequences of DNA for transcription.
