Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published July 1977 | public
Journal Article

Nucleosomes and subnucleosomes: heterogeneity and composition


Previous studies (Varshavsky, Bakayev and Georgiev, 1976a) have shown that chromatin subunits (mononucleosomes) and their oligomers in a mild staphylococcal nuclease digest of chromatin display a heterogeneous content of histone H1. We now report that a mild staphylococcal nuclease digest of either chromatin or nuclei from mouse Ehrlich tumor cells contains mononucleosomes of three discrete kinds. The smallest mononucleosome (MN₁) contains all histones except H1 and a DNA fragment 140 base pairs (bp) long. The intermediate mononucleosome (MN₂) contains all five histones and a DNA fragment 170 bp long. The third mononucleosome (MN₃) also contains all five histones, but its DNA fragment is longer and more heterogeneous in size (180–200 bp). Most of the MN₃ particles are rapidly converted by nuclease into mononucleosomes MN₁ and MN₂. There exists, however, a relatively nuclease-resistant subpopulation of the MN₃ mononucleosomes. These 200 bp MN₁ particles contain not only histones but also nonhistone proteins, and are significantly more resistant to nuclease than the bulk of MN₃ particles and the smaller mononucleosomes MN₁ and MN₂. There are eight major kinds of staphylococcal nuclease-produced soluble subnucleosomes (SN). The SN₁ is a set of naked double-stranded DNA fragments ∼20 bp long. The SN₂ is a complex of a specific basic nonhistone protein (molecular weight ∼16,000 daltons) and a DNA fragment ∼27 bp long. The SN₃ contains histone H4, the above-mentioned specific nonhistone protein and a DNA fragment ∼27 bp long. The SN4 contains histones H2a, H2b, H4 and a DNA fragment ∼45 bp long. The SN5 contains histones H2a, H2b, H3 and a DNA fragment ∼55 bp long. The SN6 is a complex of histone H1 and a DNA fragment ∼35 bp long. Subnucleosomes SN₇ and SN₈ each contain all the histones except H1, and DNA fragments ∼100 and ∼120 bp long, respectively. Nuclease digestion of isolated mono- or dinucleosomes does not produce some of the subnucleosomes. These and related findings indicate that the cleavage required to generate these subnucleosomes result from some aspect of chromatin structure which is lost upon digestion to mono- and dinucleosomes.

Additional Information

© 1977 MIT. Received 11 August 1976, Revised 8 April 1977. We thank Professor G. P. Georgiev for his support and helpful discussions during this work, and Professor H. G. Zachau, Dr. Y. V. Kozlov, P. M. Chumakov and S. Razin for gifts of Eco RII digests of mouse satellite and SV40 DNAs.

Additional details

August 19, 2023
October 23, 2023