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Description:
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During early mitosis , the sister chromatids are held together by Cohesin , a protein complex composed of Smc3 , Smc1 , Scc1 /Rad21 and Scc3 . Cohesin is first released from the arms of chromosomes , leaving it intact at the centromere . At the metaphase – anaphase transition , centromeric cohesin is cleaved , allowing the chromatids to segregate to two daughter cells . Shugoshin (Sgo -1 ) is a known protector of cohesin at the centromere . It prevents phosphorylation of cohesin complex by Plk1 before the metaphase – anaphase transition , which would otherwise lead to cohesin release , causing
the two chromatids to separate untimely .
In this study we show that Sgo1 localizes on centromeres through HP1 during interphase in human cells . Also , Sgo1 binds all three forms of HP1 (i .e . alpha , beta , gamma ) through its chromoshadow domain . We have determined the dissociation constant of this interaction to be in the sub -micromolar range . We have shown conclusively that Sgo1 binds to HP1 chromoshadow domain via one PxVxL motif .
We have further shown that , in mitosis , HP1 is recruited to centromeres by Incenp , a subunit of the chromosomal passenger complex via the chromoshadow domain of HP1 . This interaction is most likely at the HP1 CSD dimer interface , where PxVxL motifsbind . Hence , it seems that Incenp may provide competition to Sgo1 for HP1 binding . |