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J. Biol. Chem., Vol. 263, Issue 30, 15643-15651, Oct, 1988
S Chan, L Attisano and PN Lewis
Chicken erythrocyte nuclei previously incubated separately with two novel
mercury compounds (N-chloromercuribenzoyl)-biocytin and bis(p-
(chloromercuribenzoyl))-[3H]lysine diamide) were digested with micrococcal
nuclease and the digest products fractionated according to their solubility
in 0.15 M NaCl and molecular size. The identity and quantitation of the
chromatin fractions and proteins containing covalently bound mercury were
determined by Western blotting, autoradiography, and scintillation
counting. The most highly acetylated species of histone H3 in the 0.15 M
NaCl-soluble polynucleosome fraction also contained the highest proportion
of bound mercury. This fraction contains hyperacetylated core histones, is
depleted in linker histones, and enriched in nonhistone proteins. Histone
H3 in the 0.15 M NaCl-soluble mononucleosomes, which are unacetylated and
lack linker histones, was 45% less labeled than histone H3 in the 0.15 M
NaCl- soluble polynucleosome fraction. In the 0.15 M NaCl-insoluble
polynucleosomes, which contain unacetylated histones and molar proportions
of linker histones, histone H3 was 63% less labeled. Allowing for the
differential abundance of these subfractions in the nucleus, the relative
H3 reactivities are 50, 7, and 1 for 0.15 M NaCl- soluble polynucleosomes,
mononucleosomes, and 0.15 M NaCl-insoluble polynucleosomes, respectively.
Thus a gradation of reactivities exists which correlates with increasing
hyperacetylation and linker histone depletion. High mobility group proteins
1 and 2, found in subnucleosome particles in the 0.15 M NaCl-soluble
fraction, are extensively mercury- labeled. Distribution of histone
acetyltransferase activity among salt- and size-resolved micrococcal
nuclease produced fractions was almost 5- fold greater in the 0.15 M
NaCl-soluble supernatant than in the 0.15 M NaCl-insoluble pellet.
Furthermore, the acetyltransferase activity, which is tightly bound to
undigested chromatin, is rapidly released by both micrococcal nuclease and
DNase I. For short digestion times the enzyme is associated with the
salt-soluble polynucleosomes, but at longer times of digestion the enzyme
appears to be free from intact nucleosomes. The enzyme may be localized in
the globin domain in erythrocytes and maintains that region in a
hyperacetylated state which results in an altered linker histone binding
reflected in a change in the reactivity of the usually inaccessible H3
cysteine 110.
Histone H3 thiol reactivity and acetyltransferases in chicken erythrocyte nuclei
Department of Biochemistry, University of Toronto, Canada.
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