Mitotic Phosphorylation By CDK1
At mitosis, somatic H1 isoforms undergo phosphorylation at multiple cyclin-dependent kinase 1 (CDK1) consensus sites, which introduces multiple negative charges. Phosphorylation increases the affinity of H1 for mitotic chromosomes in Xenopus egg extracts and embryos, as determined by fluorescence recovery after photobleaching of wild-type H1 versus non-phosphorylable and phosphomimetic point mutants. These increases in binding affinity appear to offset the cytoplasmic dilution of H1 which occurs in mitotic cells following nuclear envelope breakdown, illustrating how the cell can regulate H1 to suit specific cellular conditions.
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