Kominami K, Seth-Smith H, Toda T
Laboratory of Cell Regulation, Imperial Cancer Research Fund, PO Box 123, 44 Lincoln's Inn Fields, London WC2A 3PX, UK.
EMBO J. 1998 Sep 15;17(18):5388-99. doi: 10.1093/emboj/17.18.5388.
Many eukaryotic cells arrest the cell cycle at G1 phase upon nutrient deprivation. In fission yeast, during nitrogen starvation, cells divide twice and arrest at G1. We have isolated a novel type of sterile mutant, which undergoes one additional S phase upon starvation and, as a result, arrests at G2. Three loci (apc10, ste9/srw1 and rum1) were identified. The apc10 mutants, previously unidentified, show, in addition to sterility, temperature-sensitive growth with defects in chromosome segregation. apc10(+) is essential for viability, encodes a conserved protein (a homologue of budding yeast Apc10/Doc1) and is required for ubiquitination and degradation of mitotic B-type cyclins. Apc10 does not co-sediment with the 20S APC-cyclosome, a ubiquitin ligase for B-type cyclins, and in the apc10 mutant the 20S complex is intact, suggesting that it is a novel regulator for this complex. A subpopulation of Apc10 does co-immunoprecipitate with the anaphase-promoting complex (APC). A second gene, ste9(+)/srw1(+), encodes a member of the fizzy-related family, also regulators of the APC. Finally, Rum1 is a cyclin-dependent kinase (CDK) inhibitor which exists only in G1. The results suggest that dual downregulation of CDK, one via the APC and the other via the CDK inhibitor, is a universal mechanism that is used to arrest cell cycle progression at G1.
许多真核细胞在营养缺乏时会在G1期停滞细胞周期。在裂殖酵母中，氮饥饿时细胞会分裂两次并停滞在G1期。我们分离出了一种新型的不育突变体，它在饥饿时会额外经历一个S期，结果停滞在G2期。鉴定出了三个基因座（apc10、ste9/srw1和rum1）。之前未被鉴定的apc10突变体，除了不育外，还表现出温度敏感型生长，且染色体分离存在缺陷。apc10(+)对细胞存活至关重要，编码一种保守蛋白（芽殖酵母Apc10/Doc1的同源物），是有丝分裂B型细胞周期蛋白泛素化和降解所必需的。Apc10不会与20S APC-环体（一种B型细胞周期蛋白的泛素连接酶）一起共沉降，在apc10突变体中20S复合物是完整的，这表明它是该复合物的一种新型调节因子。一部分Apc10确实会与后期促进复合物（APC）共免疫沉淀。第二个基因ste9(+)/srw1(+)编码一种fizzy相关家族的成员，也是APC的调节因子。最后，Rum1是一种仅存在于G1期的细胞周期蛋白依赖性激酶（CDK）抑制剂。结果表明，CDK的双重下调，一种通过APC，另一种通过CDK抑制剂，是一种普遍机制，用于使细胞周期进程在G1期停滞。
