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J. Cell Biol.,
Volume 143, Number 6, December 14, 1998 1427-1436
* Protein Section, Laboratory of Molecular Carcinogenesis, Division of Basic Sciences, National Cancer Institute, National
Institutes of Health, Bethesda, Maryland 20892; and The high mobility group 14/17 (HMG-14/
-17) proteins form specific complexes with nucleosome
core particles and produce distinct footprints on nucleosomal DNA. Therefore, they could be an integral part of the chromatin fiber. Here we show that during
the cell cycle these proteins are transiently dissociated
from chromatin. They colocalize with the nuclear DNA
in interphase and prophase but not in metaphase and
anaphase. They relocate into the nucleus and colocalize
again with the DNA in late telophase, concomitantly with the appearance of the nuclear envelope. Thus,
these nucleosomal binding proteins are not always associated with chromatin. Using reconstituted nuclei and
permeabilized cells, we demonstrate that these two
small proteins, with a molecular mass <10 kD, are actively imported into the nucleus. We identify the major
elements involved in the nuclear import of these chromosomal proteins: HMG-14/-17 proteins contain an intrinsic bipartite nuclear localization signal, and their entry into the nucleus through nuclear pores requires energy and the participation of importin Department of Cell and Developmental Biology, Biozentrum, University
of Wurzburg, Am Hubland, D-97074, Wurzburg, Germany
. These findings suggest that the cell cycle-related association of
HMG-14/-17 with chromatin is dependent on, and perhaps regulated by, nuclear import processes.
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