Mathias N, Johnson S, Byers B, Goebl M
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine and the Walther Oncology Center, Indianapolis, Indiana 46202-5122, USA.
Mol Cell Biol. 1999 Mar;19(3):1759-67. doi: 10.1128/MCB.19.3.1759.
Posttranslational modification of a protein by ubiquitin usually results in rapid degradation of the ubiquitinated protein by the proteasome. The transfer of ubiquitin to substrate is a multistep process. Cdc4p is a component of a ubiquitin ligase that tethers the ubiquitin-conjugating enzyme Cdc34p to its substrates. Among the domains of Cdc4p that are crucial for function are the F-box, which links Cdc4p to Cdc53p through Skp1p, and the WD-40 repeats, which are required for binding the substrate for Cdc34p. In addition to Cdc4p, other F-box proteins, including Grr1p and Met30p, may similarly act together with Cdc53p and Skp1p to function as ubiquitin ligase complexes. Because the relative abundance of these complexes, known collectively as SCFs, is important for cell viability, we have sought evidence of mechanisms that modulate F-box protein regulation. Here we demonstrate that the abundance of Cdc4p is subject to control by a peptide segment that we term the R-motif (for "reduced abundance"). Furthermore, we show that binding of Skp1p to the F-box of Cdc4p inhibits R-motif-dependent degradation of Cdc4p. These results suggest a general model for control of SCF activities.
蛋白质经泛素进行的翻译后修饰通常会导致泛素化蛋白质被蛋白酶体快速降解。泛素转移至底物是一个多步骤过程。Cdc4p是泛素连接酶的一个组分，它将泛素结合酶Cdc34p与其底物相连。在Cdc4p中对其功能至关重要的结构域包括F-box，它通过Skp1p将Cdc4p与Cdc53p相连，以及WD-40重复序列，它是结合Cdc34p底物所必需的。除Cdc4p外，其他F-box蛋白，包括Grr1p和Met30p，可能同样与Cdc53p和Skp1p共同作用，作为泛素连接酶复合体发挥功能。由于这些统称为SCF的复合体的相对丰度对细胞活力很重要，我们一直在寻找调节F-box蛋白调控机制的证据。在此我们证明，Cdc4p的丰度受一个我们称为R基序（“reduced abundance”，即“降低丰度”之意）的肽段控制。此外，我们表明Skp1p与Cdc4p的F-box结合会抑制Cdc4p的R基序依赖性降解。这些结果提示了一个控制SCF活性的通用模型。
