Minc E, Allory Y, Worman H J, Courvalin J C, Buendia B
Departement de Biologie Cellulaire, Institut Jacques Monod, CNRS, Université Paris 7, Paris, France.
Chromosoma. 1999 Aug;108(4):220-34. doi: 10.1007/s004120050372.
Mammalian heterochromatin proteins 1 (HP1alpha, HP1beta, and HP1gamma) are nonhistone proteins that interact in vitro with a set of proteins that play a role in chromatin silencing, transcription, and chromatin remodeling. Using antibodies specific for each HP1 isoform, we showed that they segregate in distinct nuclear domains of human HeLa cells. By contrast, in mouse 3T3 interphase cells, HP1alpha and HP1beta are strictly colocalized. In mitotic HeLa cells, all of HP1alpha and a fraction of HP1beta and HP1gamma remain associated with chromosomes. Immunostaining of spread HeLa chromosomes showed that HP1alpha is mainly localized on centromeres as shown previously for HP1beta, while HP1gamma is distributed on discrete sites on the arms of chromosomes. Biochemical analysis showed that HP1alpha and HP1gamma are phosphorylated throughout the cell cycle, although more extensively in mitosis than in interphase, while HP1beta apparently remains unphosphorylated. Therefore, despite their extensive sequence conservation, mammalian HP1 isoforms differ widely in their nuclear localization, mitotic distribution and cell cycle-related phosphorylation. Thus, subtle differences in primary sequence and in posttranslational modifications may promote their targeting at different chromatin sites, generating pleiotropic effects.
哺乳动物异染色质蛋白1（HP1α、HP1β和HP1γ）是非组蛋白，它们在体外与一组在染色质沉默、转录和染色质重塑中起作用的蛋白质相互作用。使用针对每种HP1亚型的特异性抗体，我们发现它们在人类HeLa细胞的不同核区域中分离。相比之下，在小鼠3T3间期细胞中，HP1α和HP1β严格共定位。在有丝分裂的HeLa细胞中，所有的HP1α以及一部分HP1β和HP1γ仍与染色体相关。对铺展的HeLa染色体进行免疫染色显示，HP1α主要定位于着丝粒，如先前对HP1β的研究所示，而HP1γ分布于染色体臂上的离散位点。生化分析表明，HP1α和HP1γ在整个细胞周期中都被磷酸化，尽管在有丝分裂期比在间期更广泛，而HP1β显然保持未磷酸化状态。因此，尽管它们的序列具有广泛的保守性，但哺乳动物HP1亚型在核定位、有丝分裂分布和细胞周期相关的磷酸化方面存在很大差异。因此，一级序列和翻译后修饰的细微差异可能促使它们靶向不同的染色质位点，产生多效性作用。
