G1 phase-dependent nucleolar accumulation of human histone H1x |
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Authors: | Stoldt Stefan Wenzel Dirk Schulze Ekkehard Doenecke Detlef Happel Nicole |
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Affiliation: | 1. Institute for Biochemistry and Molecular Cell Biology, University of G?ttingen, Humboldtallee 23, 37073 G?ttingen, Germany;2. Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, 37077 G?ttingen, Germany;3. Institute for Biology III, Bioinformatics and Molecular Genetics, Albert‐Ludwigs‐University, Schaenzlestrasse 1, 79104 Freiburg, Germany |
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Abstract: | Background information: H1 histones are a protein family comprising several subtypes. Although specific functions of the individual subtypes could not be determined so far, differential roles are indicated by varied nuclear distributions as well as differential expression patterns of the H1 subtypes. Although the group of replication‐dependent H1 subtypes is synthesized during S phase, the replacement H1 subtype, H1°, is also expressed in a replication‐independent manner in non‐proliferating cells. Recently we showed, by protein biochemical analysis, that the ubiquitously expressed subtype H1x is enriched in the micrococcal nuclease‐resistant part of chromatin and that, although it shares common features with H1°, its expression is differentially regulated, since, in contrast to H1°, growth arrest or induction of differentiation did not induce an accumulation of H1x. Results: In the present study, we show that H1x exhibits a cell‐cycle‐dependent change of its nuclear distribution. This H1 subtype showed a nucleolar accumulation during the G1 phase, and it was evenly distributed in the nucleus during S phase and G2. Immunocytochemical analysis of the intranucleolar distribution of H1x indicated that it is located mainly in the condensed nucleolar chromatin. In addition, we demonstrate that the amount of H1x protein remained nearly unchanged during S phase progression, which is in contrast to the replication‐dependent subtypes. Conclusion: These results suggest that the differential localization of H1x provides a mechanism for a control of H1x activity by means of shuttling between nuclear subcompartments instead of a controlled turnover of the protein. |
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Keywords: | cell cycle histone H1 histone H1x nuclear localization nucleolus |
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