Wolf D A, McKeon F, Jackson P K
Departments of Pathology and Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305, USA.
Curr Biol. 1999 Apr 8;9(7):373-6. doi: 10.1016/s0960-9822(99)80165-1.
Ubiquitin-dependent proteolysis plays an important role in cell-cycle control [1] [2]. In budding yeast, the protein Skp1p, the cullin-family member Cdc53p, and the F-box/WD-repeat protein Cdc4p form the SCFCdc4p ubiquitin ligase complex, which targets the cyclin-dependent kinase (Cdk) inhibitor Sic1p for proteolysis [3] [4] [5] [6] [7] [8]. Sic1p is recruited to the SCFCdc4p complex by binding to the WD-repeat region of Cdc4p [5] [6], while Skp1p binds to the F-box of Cdc4p [9]. In fission yeast, two distinct Cdc4p-related proteins, Pop1p/Ste16p [10] [11] and the recently identified Sud1p/Pop2p [12], regulate the stability of the replication initiator Cdc18p and the Cdk inhibitor Rum1p. We show here that, despite their structural and functional similarities, the pop1 and pop2 genes fail to complement each other's deletion phenotypes, indicating that they perform non-redundant, but potentially interdependent, functions in proteolysis. Consistent with this hypothesis, Pop1p and Pop2p formed heterooligomeric complexes when overexpressed, and binding of Cdc18p to Pop2p was dependent on Pop1p. The Pop1p-Pop2p interaction was mediated by the amino-terminal domain of Pop2p which, when fused to full-length Pop1p, rescued the phenotype of a Deltapop1Deltapop2 double mutant. Thus, close physical proximity of two distinct F-box/WD-repeat proteins directs proteolysis mediated by the SCFPop ubiquitin ligase complex.
泛素依赖性蛋白水解在细胞周期调控中发挥着重要作用[1][2]。在芽殖酵母中，蛋白质Skp1p、cullin家族成员Cdc53p以及F-box/WD重复蛋白Cdc4p形成SCFCdc4p泛素连接酶复合物，该复合物靶向细胞周期蛋白依赖性激酶（Cdk）抑制剂Sic1p进行蛋白水解[3][4][5][6][7][8]。Sic1p通过与Cdc4p的WD重复区域结合而被招募到SCFCdc4p复合物中[5][6]，而Skp1p则与Cdc4p的F-box结合[9]。在裂殖酵母中，两种不同的Cdc4p相关蛋白，Pop1p/Ste16p[10][11]和最近鉴定出的Sud1p/Pop2p[12]，调节复制起始因子Cdc18p和Cdk抑制剂Rum1p的稳定性。我们在此表明，尽管pop1和pop2基因在结构和功能上具有相似性，但它们不能互补彼此的缺失表型，这表明它们在蛋白水解中发挥非冗余但可能相互依赖的功能。与该假设一致，Pop1p和Pop2p在过表达时形成异源寡聚复合物，并且Cdc18p与Pop2p的结合依赖于Pop1p。Pop1p-Pop2p相互作用由Pop2p的氨基末端结构域介导，当该结构域与全长Pop1p融合时，可挽救Δpop1Δpop2双突变体的表型。因此，两种不同的F-box/WD重复蛋白的紧密物理接近指导了由SCFPop泛素连接酶复合物介导的蛋白水解。
