Nonrandom location of H1-H1 degree histones on chromatin of mouse liver and brain.

The electrophoretic behavior of nucleosome dimers reconstituted with H1 or H1 degrees and the features of the digestion of those reconstituted dimers with micrococcal nuclease were first investigated. Both criteria appear to support the notion that H1 degrees can replace H1 on the nucleosome on a one-to-one basis and that both proteins fulfill a similar structural role in chromatin. H1/H1 degrees ratios in different chromatin subfractions from mouse liver were then indirectly measured by means of an electrophoretic purification of H1 degrees- from H1-containing nucleosome monomers, followed by a titration of different specific nucleotide sequences in the corresponding DNAs. Satellite and globin containing chromatin subfractions were found to contain only about half the amount of H1 degrees which is normally encountered in bulk chromatin, indicating a nonrandom location of H1-H1 degrees variants on untranscribed sequences; in contrast, titrations with cDNA from poly(A+) RNA and albumin cDNA show an approximately 2-fold enrichment in H1 degrees for the corresponding chromatin when compared to the same bulk chromatin. In the brain, inactive albumin chromatin contains a relative amount of both H1 variants similar to that found in satellite or globin chromatin in liver. Amounts of H1 degrees can, therefore, be correlated with different states of chromatin: an inactive state with a lower amount of H1 degrees and a potentially active state with an enrichment in H1 degrees.