Heo S J, Tatebayashi K, Ikeda H
Department of Molecular Biology, University of Tokyo, Japan.
Curr Genet. 1999 Dec;36(6):329-38. doi: 10.1007/s002940050507.
Cohesin is a protein that plays a key role in the cohesion and separation of sister chromatids. During the duplication of chromatids, cohesin holds sister chromatids together until the onset of anaphase, and thereby prevents the premature separation of sister chromatids which would otherwise jeopardize the faithful segregation of chromosomes. To investigate the molecular mechanisms of sister chromatid cohesion, we have isolated multicopy suppressors of a temperature-sensitive (ts) mutation in the SCC1/MCD1/RHC21 gene which encodes a component of the cohesin complex in budding yeast. Isolation of multicopy suppressors of rhc21-sk16 and further genetic analyses revealed that several distinct biological pathways are involved in the regulation of SCC1/MCD1/RHC21 function. Firstly, PDE2 and BCY1, each of which inhibits the activity of protein kinase A (PKA), suppressed the temperature sensitivity of the rhc21-sk16 mutant. Secondly, PDE2 suppressed the temperature sensitivity of the cdc16-1 mutant. These results suggest that SCC1/MCD1/RHC21 is negatively regulated by the PKA pathway via the anaphase promoting complex (APC). Thirdly, ZDS1, a multicopy suppressor of cdc28-1N, and its homologue ZDS2 were isolated as multicopy suppressors of rhc21-sk16. Furthermore, the rhc21-sk16 mutant did not grow in the presence of the cdc28-1N mutation. Hence, SCC1/MCD1/RHC21 is positively regulated by the mitotic CDK, CDC28. Finally, SCC1/MCD1/RHC21 was found to interact genetically with CDC20, an activator of APC. Overexpression of CDC20 suppressed the temperature sensitivity of rhc21-sk16, and rhc21-sk16 was shown to be synthetically lethal with cdc20-1. In addition, the growth of the rhc21-sk16 mutant was inhibited by overproduction of the anaphase inhibitor Pds1p, whose degradation is mediated by Cdc20p in APC-dependent proteolysis. The functional relationships between SCC1/MCD1/RHC21 and PKA, CDK or APC are discussed.
黏连蛋白是一种在姐妹染色单体的黏连和分离过程中起关键作用的蛋白质。在染色单体复制期间，黏连蛋白将姐妹染色单体维系在一起直至后期开始，从而防止姐妹染色单体过早分离，否则这将危及染色体的准确分离。为了研究姐妹染色单体黏连的分子机制，我们分离了酿酒酵母中编码黏连蛋白复合体一个组分的SCC1/MCD1/RHC21基因温度敏感（ts）突变的多拷贝抑制子。rhc21-sk16多拷贝抑制子的分离及进一步的遗传学分析表明，几种不同的生物学途径参与了SCC1/MCD1/RHC21功能的调控。首先，PDE2和BCY1，它们各自抑制蛋白激酶A（PKA）的活性，抑制了rhc21-sk16突变体的温度敏感性。其次，PDE2抑制了cdc16-1突变体的温度敏感性。这些结果表明，SCC1/MCD1/RHC21通过后期促进复合体（APC）受PKA途径的负调控。第三，ZDS1，cdc28-1N的多拷贝抑制子，及其同源物ZDS2被分离为rhc21-sk16的多拷贝抑制子。此外，rhc21-sk16突变体在存在cdc28-1N突变的情况下无法生长。因此，SCC1/MCD1/RHC21受有丝分裂周期蛋白依赖性激酶CDC28的正调控。最后，发现SCC1/MCD1/RHC21与APC的激活因子CDC20存在遗传学相互作用。CDC20的过表达抑制了rhc21-sk16的温度敏感性，并且rhc21-sk16与cdc20-1表现为合成致死。此外，后期抑制因子Pds1p的过量产生抑制了rhc21-sk16突变体的生长，其降解由APC依赖性蛋白酶解中的Cdc20p介导。文中讨论了SCC1/MCD1/RHC21与PKA、CDK或APC之间的功能关系。
