| Budget Amount *help |
¥15,100,000 (Direct Cost: ¥15,100,000)
Fiscal Year 2005: ¥4,400,000 (Direct Cost: ¥4,400,000)
Fiscal Year 2004: ¥4,400,000 (Direct Cost: ¥4,400,000)
Fiscal Year 2003: ¥6,300,000 (Direct Cost: ¥6,300,000)
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| Research Abstract |
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.
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