| Summary: | 碩士 === 慈濟大學 === 微免暨分子醫學研究所 === 98 === Cell division cycle can be divided into four phases: G1, S, G2 and M. Cyclin-dependent kinase complex is a key regulator for cell cycle progression. Cyclin proteolysis may lead to inactivation of CDK activity. In Saccharomyces cerevisiae, both SCF and APC/C are required to promote cyclin protoelysis. SCF complex regulates proteolysis of Cln1-3 and Clb6 whereas APC/C complex does proteolysis of Clb1-5.
We found that not only SCFcdc4 required for Clb6 proteolysis, but APC/C during G1 transition to S. Furthermore, the co-factor of APC/C was Cdh1 not Cdc20 in Clb6 proteolysis. In Clb6, there are two specific residue, KEN box and D-box (destruction box). When Clb6 lost the two specific residue, APCCdh1 couldn’t detect Clb6 to do the job. In addition, we proved APCCdh1 didn’t involve Clb6 proteolysis in S phase. So we suggested that APCCdh1 was working in G1 phase, SCFcdc4 was working in S phase. We were experimenting with Clb6mkb,mdb and Clb6 by time-cross analyzing, actually, expression of Clb6mkb,mdb could result in an earlier DNA replication, bud growth, and entry into mitosis. The result suggest that Clb6 maybe an important index of entry into S phase.
In early anaphase, FEAR network (Cdc Fourteen Early Anaphase Release) is active to promote release of a small portion of the phosphatase Cdc14 from nucleolus to nucleus. In late anaphase, the mitotic exit network (MEN) can promote release of all the Cdc14 proteins from nucleolus for activation of APCCdh1 and Sic1. Active APCCdh1 promotes proteolysis of mitotic cyclin for completion of mitosis, and Sic1 inhibited cyclin dependent kinase (CDK). Our lab isolated a new temperature-sensitive mutant, cdc14A280V. After prolonged arrest, cdc14A280V mutant could form apical projection and DNA re-replication. Deletion of CLB1 could enhance apical projection formation and DNA re-replication in cdc14A280V cells. Interestingly, overexpression of Clb3 could induce formation of apical projection through Swe1-depedent and Swe1-independent mechanisms at the permissive temperature.
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