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J. Cell Biol.,
Volume 145, Number 2, April 19, 1999 225-235
* Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
V6T 1Z3; and The NH2-terminal domain (N-tail) of histone
H3 has been implicated in chromatin compaction and
its phosphorylation at Ser10 is tightly correlated with
mitotic chromosome condensation. We have developed
one mAb that specifically recognizes histone H3 N-tails
phosphorylated at Ser10 (H3P Ab) and another that
recognizes phosphorylated and unphosphorylated H3
N-tails equally well (H3 Ab). Immunocytochemistry
with the H3P Ab shows that Ser10 phosphorylation begins in early prophase, peaks before metaphase, and decreases during anaphase and telophase. Unexpectedly,
the H3 Ab shows stronger immunofluorescence in mitosis than interphase, indicating that the H3 N-tail is
more accessible in condensed mitotic chromatin than in
decondensed interphase chromatin. In vivo ultraviolet laser cross-linking indicates that the H3 N-tail is bound
to DNA in interphase cells and that binding is reduced
in mitotic cells. Treatment of mitotic cells with the protein kinase inhibitor staurosporine causes histone H3
dephosphorylation and chromosome decondensation. It also decreases the accessibility of the H3 N-tail to H3
Ab and increases the binding of the N-tail to DNA.
These results indicate that a phosphorylation-dependent weakening of the association between the H3
N-tail and DNA plays a role in mitotic chromosome condensation.
ONCOR, Inc., Gaithersburg, Maryland 20877
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