|Budget Amount *help
¥7,100,000 (Direct Cost : ¥7,100,000)
Fiscal Year 1997 : ¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1996 : ¥1,900,000 (Direct Cost : ¥1,900,000)
Fiscal Year 1995 : ¥3,200,000 (Direct Cost : ¥3,200,000)
Rapid protein degradation catalyzed by the ubiquitin-dependent pathway has been shown to be involoved in cellular regulation such as cell cycle control, DNA repair, stress response and transcriptional control. Ubiquitination of proteins is a multiple enzymatic process with ubipuitin-activating enzyme (E1), ubipuitin-conjugating enzyme (E2) and ubiquitin ligase (E3). Most cells contain a single E1, but E2 exists as a family of enzyemes. In budding yeast, 13 genes for E2 have been identified to be involved in defferent cellular functions. Different classes of E3 have been identified. Thus, responsible E2, along with its partner E3, recognizes and catalyzes the conjugation of ubiquitin to a specific substrate.
Mitosis is initiated by synthesis and the accumulation of mitotic cyclin. For the exit from mitosis, degradation of mitotic cyclin is necessary. Cyclin-specific E3 has been identified biochemically as a large complex, termed cyclosome or APC.APC is also required at the onset of anaphase for degradation of protein (s) essential for sister chromatid pairing during metaphase.
E2 responsible for ubiquitination of cyclin B,has been identified as UBC-xin Xenopus egg extract and E2-cin clam egg extract. Analysis of their cDNAs revealed that they are homoiogous to each other but not to any of the E2s identified so far in budding yeast and other species. Among newly isolated genes in this PROJECT of E2 in Schizosaccharomyces pombe, ubcP4+ was found to be highly homologous to UBC-x and E2-c, and proved to be essential for the transition from metaphase to anaphase in mitosis. Cdc13, a mitotic cyclin of the fission yeast, was stabilized in UbcP4-depleted cells. Overproduction of UbcP4 in the cell specifically suppressed the temperature-sensitive mutation defect in the component of APC,suggesting that UbcP4 mediates the ubiquitin pathway specific to APC.