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

凝集素是一种由SMC异源二聚体(SMC2/CAP-E和SMC4/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质复合体，在体内有丝分裂染色体凝聚中起重要作用。凝聚素在体外利用ATP水解酶的能量，在Topo I存在的情况下诱导DNA的正超卷曲。除了有丝分裂功能外，凝聚素还参与间期染色质的调节，如DNA修复、损伤检查点反应和转录调节。凝集素亚基的蛋白质水平和稳定性在整个细胞周期中几乎是恒定的。凝聚素在有丝分裂过程中被CDc2磷酸化，在间期被CK2磷酸化。与镉诱导的凝聚素I的磷酸化对超螺旋的刺激作用不同，CK2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的磷酸化在空间和时间上受到不同于Cdc2介导的磷酸化的调节：CK2依赖的磷酸化在间期增加，在有丝分裂期间染色体上的磷酸化减少。这些发现首次证明了凝聚素I的负调控模式，这一过程可能会影响间期和有丝分裂过程中的染色质结构。当凝聚素加入体外转录系统时，转录水平降低，这种抑制被CK2介导的磷酸化所取消。因此，有可能染色质结构在间期被凝集素压缩，而CK2介导的磷酸化抑制凝集素活性导致染色质结构松弛和反式激活。

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.