Limited action of micrococcal nuclease on trout testis nuclei generates two mononucleosome subsets enriched in transcribed DNA sequences.

Abstract

Hybridization experiments show that DNA extracted from 2 distinct subsets of mononucleosomes (MN1 and NM2) generated by a limited action of micrococcal nuclease on trout testis nuclei is enriched .apprx. 7-fold in sequences that are transcribed into cytoplasmic polyadenylated RNA in trout testis cells. Both subsets of mononucleosomes contain 8 core small, basic, high-mobility-group (HMG) protein H6 [Levy et al., (1979)], bound to a DNA fragment of 140 base pairs [bp] MN2 contains 1 molecule of H1 but no H6, and its DNA length is somewhat longer at 140-190 bp. The preferential release of these 2 subsets of mononucleosomes is correlated with the presence of a 2nd larger HMG protein, HMG-T, in the linker regions flanking both types of mononucleosomes. The HMG-T-containing linker regions appear to be considerably more susceptible to attack by micrococcal nuclease than H1-containing linkers. Cross-reassociation reactions between the DNA from MN1 and MN2 subsets indicate that they share a significant extent of sequence overlap but also that each subset contains specific sequences that are absent in the other subset.