Patton E E, Willems A R, Sa D, Kuras L, Thomas D, Craig K L, Tyers M
Programme in Molecular Biology and Cancer, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Canada M5G 1X5.
Genes Dev. 1998 Mar 1;12(5):692-705. doi: 10.1101/gad.12.5.692.
In budding yeast, ubiquitination of the cyclin-dependent kinase (Cdk) inhibitor Sic1 is catalyzed by the E2 ubiquitin conjugating enzyme Cdc34 in conjunction with an E3 ubiquitin ligase complex composed of Skp1, Cdc53 and the F-box protein, Cdc4 (the SCFCdc4 complex). Skp1 binds a motif called the F-box and in turn F-box proteins appear to recruit specific substrates for ubiquitination. We find that Skp1 interacts with Cdc53 in vivo, and that Skp1 bridges Cdc53 to three different F-box proteins, Cdc4, Met30, and Grr1. Cdc53 contains independent binding sites for Cdc34 and Skp1 suggesting it functions as a scaffold protein within an E2/E3 core complex. F-box proteins show remarkable functional specificity in vivo: Cdc4 is specific for degradation of Sic1, Grr1 is specific for degradation of the G1 cyclin Cln2, and Met30 is specific for repression of methionine biosynthesis genes. In contrast, the Cdc34-Cdc53-Skp1 E2/E3 core complex is required for all three functions. Combinatorial control of SCF complexes may provide a basis for the regulation of diverse cellular processes.
在芽殖酵母中，细胞周期蛋白依赖性激酶（Cdk）抑制剂Sic1的泛素化由E2泛素结合酶Cdc34与由Skp1、Cdc53和F-box蛋白Cdc4组成的E3泛素连接酶复合物（SCFCdc4复合物）共同催化。Skp1结合一个称为F-box的基序，反过来，F-box蛋白似乎招募特定的底物进行泛素化。我们发现Skp1在体内与Cdc53相互作用，并且Skp1将Cdc53与三种不同的F-box蛋白Cdc4、Met30和Grr1连接起来。Cdc53含有Cdc34和Skp1的独立结合位点，这表明它在E2/E3核心复合物中作为一种支架蛋白发挥作用。F-box蛋白在体内表现出显著的功能特异性：Cdc4特异性降解Sic1，Grr1特异性降解G1期细胞周期蛋白Cln2，Met30特异性抑制甲硫氨酸生物合成基因。相比之下，所有这三种功能都需要Cdc34-Cdc53-Skp1 E2/E3核心复合物。SCF复合物的组合控制可能为多种细胞过程的调控提供基础。
