Distribution of high mobility group proteins among domains of trout testis chromatin differing in their susceptibility to micrococcal nuclease.

Trout testis nuclei were treated with micrococcal nuclease, an enzyme which is known to digest preferentially the linker regions in transcriptionally competent portions of the chromatin. The digested nuclei were fractionated by two different methods, and the distribution of histones and high mobility group proteins among the various fractions was quantitated. The results obtained indicate that the linker regions of transcriptionally active nucleosomes are depleted in H1 and enriched in HMG (high mobility group)-T and ubiquitin. The core particles in transcribed regions of the chromatin are depleted in unacetylated H4 and enriched in the highly acetylated forms of H4 and also in the small basic non-histone, H6. Our results also suggest that one-fourth of the total H6 and one-half of the total HMG-T of chromatin are present in a different domain probably comprising nontranscribed regions.