Functional analysis of budding yeast Cullin based E3

蛋白质降解通过泛素-蛋白酶体系统调节多种细胞过程。在出芽酵母中，cullin蛋白家族包括三个成员：Cdc53、Cul3和Cul8。最近我们报道Lag2是一种新的SCF复合物调节因子。在本研究中，我们对Lag2、Cul3和Cul8进行了功能分析。我们发现Lag2上的赖氨酸K16是Rub1偶联的靶标，而Dcn1是该反应所必需的。与野生型Lag2一样，Lag2 K16R突变体也负向调节SCF功能，这表明Lag2的功能不需要Rub1与Lag2结合。在出芽酵母中，BTB蛋白家族包括四个成员。我们鉴定了一个BTB蛋白，Yil001w是Cul3结合蛋白，Okp1是Cul3型E3的候选蛋白。此外，我们还鉴定了一些蛋白作为Cul8结合蛋白。这些观察结果表明Cul3和Cul8形成复合物并作为E3泛素连接酶起作用。

Protein degradation via ubiquitin-proteasome system regulates a variety of cellular processes. In budding yeast, the cullin protein family includes three members: Cdc53, Cul3, and Cul8. Recently we have reported Lag2 as a novel regulator of SCF complex. In this study, we performed the functional analysis of Lag2, Cul3 and Cul8. We identify that a single lysine, K16, on Lag2 is a target of Rub1 conjugation and Dcn1 is required for this reaction. Like wild-type Lag2, Lag2 K16R mutant also negatively modulates the SCF function, indicating that Rub1 conjugation to Lag2 is not required for the function of Lag2. In budding yeast, the BTB protein family includes four members. We identify a BTB protein, Yil001w as a Cul3 binding protein and Okp1 as a candidate of Cul3-type E3. Furthermore, we identify several proteins as Cul8 binding proteins. These observations indicate that Cul3 and Cul8 form complexes and function as E3 ubiquitin ligases.