The Journal of Cell Biology, Vol 79, 97-109, Copyright © 1978 by The Rockefeller University Press
Fractionation of nucleosomes by salt elution from micrococcal nuclease- digested nuclei
MM Sanders
The solubilization of nucleosomes and histone H1 with increasing
concentrations of NaCl has been investigated in rat liver nuclei that had
been digested with micrococcal nuclease under conditions that did not
substantially alter morphological properties with respect to differences in
the extent of chromatin condensation. The pattern of nucleosome and H1
solubilization was gradual and noncoordinate and at least three different
types of nucleosome packing interactions could be distinguished from the
pattern. A class of nucleosomes containing 13-- 17% of the DNA and
comprising the chromatin structures most available for micrococcal nuclease
attack was eluted by 0.2 M NaCl. This fraction was solubilized with an
acid-soluble protein of apparent molecular weight of 20,000 daltons and no
histone H1. It differed from the nucleosomes released at higher NaCl
concentrations in content of nonhistone chromosomal proteins. 40--60% of
the nucleosomes were released by 0.3 M NaCl with 30% of the total nuclear
histone H1 bound. The remaining nucleosomes and H1 were solublized by 0.4 M
or 0.6 M NaCl. H1 was not nucleosome bound at these ionic strengths, and
these fractions contained, respectively, 1.5 and 1.8 times more H1 per
nucleosome than the population released by 0.3 M NaCl. These fractions
contained the DNA least available for micrococcal nuclease attach. The
strikingly different macromolecular composition, availability for nuclease
digestion, and strength of the packing interactions of the nucleosomes
released by 0.2 M NaCl suggest that this population is involved in a
special function.
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