Analysis of the cell cycle regulation of chromosome condensation protein complex, condensin.

凝聚素是由SMC异源二聚体（SMC 2/CAP-E和SMC 4/CAP-E）和其他三个非SMC亚基（CAP-D2、-G和-H）组成的保守的五聚体蛋白复合物，在体内有丝分裂染色体凝聚中起重要作用。在体外，在topo I存在下，凝聚素利用ATP水解的能量诱导正超螺旋进入DNA。除了有丝分裂功能外，凝聚素还参与了细胞分裂间期的染色质调控，如DNA修复、损伤检查点反应和转录调控等。在整个细胞周期中，凝聚素亚基的蛋白水平和稳定性几乎是恒定的。在有丝分裂期间，由Cdc 2磷酸化缩合蛋白，并在间期由CK 2磷酸化。与Cdc 2诱导的凝聚素I磷酸化对超螺旋的刺激作用相反，CK 2的磷酸化降低了凝聚素I的超螺旋活性。CK 2介导的凝聚素I磷酸化在空间和时间上以与Cdc 2介导的磷酸化不同的方式进行调节：CK 2依赖的磷酸化在间期增加，在有丝分裂期间在染色体上减少。这些发现首次证实了凝聚素I在细胞分裂间期和有丝分裂期对染色质结构的负调控模式，当凝聚素I加入体外转录系统中时，转录水平降低，而这种抑制作用被CK 2介导的磷酸化所抵消。因此，这是可能的染色质结构紧凑的凝聚素在间期，和抑制凝聚素活性的CK 2介导的磷酸化导致松弛的染色质结构和反式激活。

Condensin, a conserved pentameric protein complex composed of SMC heterodimer (SMC2/CAP-E and SMC4/CAP-E) and three other non-SMC subunits (CAP-D2, -G, and -H), plays an essential role in mitotic chromosome condensation in vivo. Condensin induces positive supercoiling into DNA in the presence of topo I using the energy of ATP hydrolysis in vitro. In addition to their mitotic functions, condensins have been implicated in chromatin regulation during interphase, such as DNA repair, damage checkpoint response and transcriptional regulation.We analyzed precisely cell cycle regulation of condensin complex. The protein levels and stabilities of condensin subunits were almost constant throughout the cell cycle. Condensin was phosphorylated by Cdc2 during mitosis, and by CK2 during interphase. In contrast to the 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.When condensin was added into in vitro transcription system, transcription level was reduced, and the suppression was cancelled by the CK2-mediated phosphorylation. Thus, it is possible chromatin structure was compacted by condensin during interphase, and inhibition of condensin activity by the CK2-mediated phosphorylation leads to relaxation of chromatin structure and transactivation.