Kramer K M, Fesquet D, Johnson A L, Johnston L H
Division of Yeast Genetics, National Institute for Medical Research, London, UK.
EMBO J. 1998 Jan 15;17(2):498-506. doi: 10.1093/emboj/17.2.498.
SIC1 is a non-essential gene encoding a CDK inhibitor of Cdc28-Clb kinase activity. Sic1p is involved in both mitotic exit and the timing of DNA synthesis. To identify other genes involved in controlling Clb-kinase activity, we have undertaken a genetic screen for mutations which render SIC1 essential. Here we describe a gene we have identified by this means, RSI1/APC2. Temperature-sensitive rsi1/apc2 mutants arrest in metaphase and are unable to degrade Clb2p, suggesting that Rsi1p/Apc2p is associated with the anaphase promoting complex (APC). This is an E3 ubiquitin-ligase that controls anaphase initiation through degradation of Pds1p and mitotic exit via degradation of Clb cyclins. Indeed, the anaphase block in rsi1/apc2 temperature-sensitive mutants is overcome by removal of PDS1, consistent with Rsi1p/Apc2p being part of the APC. In addition, like our rsi1/apc2 mutations, cdc23-1, encoding a known APC subunit, is also lethal with sic1Delta. Thus SIC1 clearly becomes essential when APC function is compromised. Finally, we find that Rsi1p/Apc2p co-immunoprecipitates with Cdc23p. Taken together, our results suggest that RSI1/APC2 is a subunit of APC.
SIC1是一个非必需基因，编码一种抑制Cdc28-Clb激酶活性的细胞周期蛋白依赖性激酶（CDK）。Sic1p参与有丝分裂退出和DNA合成的时间调控。为了鉴定其他参与控制Clb激酶活性的基因，我们针对使SIC1成为必需基因的突变进行了遗传筛选。在此，我们描述了一个通过这种方法鉴定出的基因RSI1/APC2。温度敏感型rsi1/apc2突变体在中期停滞，无法降解Clb2p，这表明Rsi1p/Apc2p与后期促进复合物（APC）相关。APC是一种E3泛素连接酶，通过降解Pds1p来控制后期起始，并通过降解Clb细胞周期蛋白来控制有丝分裂退出。实际上，通过去除PDS1可克服rsi1/apc2温度敏感型突变体中的后期阻滞，这与Rsi1p/Apc2p是APC的一部分相一致。此外，与我们的rsi1/apc2突变一样，编码已知APC亚基的cdc23-1与sic1Delta也是致死组合。因此，当APC功能受损时，SIC1显然变得必不可少。最后，我们发现Rsi1p/Apc2p与Cdc23p共免疫沉淀。综上所述，我们的结果表明RSI1/APC2是APC的一个亚基。
