Takemoto Ai, Kimura Keiji, Yanagisawa Junn, Yokoyama Shigeyuki, Hanaoka Fumio
Cellular Physiology Laboratory, Discovery Research Institute, RIKEN, Wako, Saitama, Japan.
EMBO J. 2006 Nov 15;25(22):5339-48. doi: 10.1038/sj.emboj.7601394. Epub 2006 Oct 26.
Condensin I, which plays an essential role in mitotic chromosome assembly and segregation in vivo, constrains positive supercoils into DNA in the presence of adenosine triphosphate in vitro. Condensin I is constitutively present in a phosphorylated form throughout the HeLa cell cycle, but the sites at which it is phosphorylated in interphase cells differ from those recognized by Cdc2 during mitosis. Immunodepletion, in vitro phosphorylation, and immunoblot analysis using a phospho-specific antibody suggested that the CK2 kinase is likely to be responsible for phosphorylation of condensin I during interphase. In contrast to the slight stimulatory effect of Cdc2-induced phosphorylation of condensin I on supercoiling, phosphorylation by CK2 reduced the supercoiling activity of condensin I. CK2-mediated phosphorylation of condensin I is spatially and temporally regulated in a manner different to that of Cdc2-mediated phosphorylation: CK2-dependent phosphorylation increases during interphase and decreases on chromosomes during mitosis. These findings are the first to demonstrate a negative regulatory mode for condensin I, a process that may influence chromatin structure during interphase and mitosis.
凝聚素I在体内有丝分裂染色体组装和分离过程中发挥着至关重要的作用，在体外，它在三磷酸腺苷存在的情况下将正超螺旋引入DNA。凝聚素I在整个HeLa细胞周期中以磷酸化形式持续存在，但它在间期细胞中被磷酸化的位点与有丝分裂期间Cdc2识别的位点不同。免疫耗竭、体外磷酸化以及使用磷酸特异性抗体进行的免疫印迹分析表明，CK2激酶可能在间期负责凝聚素I的磷酸化。与Cdc2诱导的凝聚素I磷酸化对超螺旋的轻微刺激作用相反，CK2介导的磷酸化降低了凝聚素I的超螺旋活性。CK2介导的凝聚素I磷酸化在空间和时间上的调节方式与Cdc2介导的磷酸化不同：CK2依赖性磷酸化在间期增加，在有丝分裂期间在染色体上减少。这些发现首次证明了凝聚素I的负调控模式，这一过程可能在间期和有丝分裂期间影响染色质结构。
