Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Strasse 10, D-35043 Marburg, Germany.
Mol Microbiol. 2011 Sep;81(6):1484-98. doi: 10.1111/j.1365-2958.2011.07783.x. Epub 2011 Aug 4.
In mammalian cells RACK1 serves as a scaffold protein that has a role in integrating inputs from different signalling pathways and affects translation through association with ribosomes. Ustilago maydis contains a seven-WD40 repeat motif protein designated Rak1, which shows 68% identity to RACK1 and 51% identity to Asc1p of Saccharomyces cerevisiae. An asc1 mutant could be complemented by introduction of U. maydis rak1. The deletion of rak1 affected cell growth, cell wall integrity and specifically attenuated cell fusion. This latter defect was caused by reduced expression of prf1 encoding the regulator for pheromone (mfa) and pheromone-receptor genes. Rak1 interacts with a variety of ribosomal proteins and microarray analysis revealed that the deletion of rak1 led to severely reduced expression of rop1, a transcriptional activator of prf1. The constitutive expression of rop1 could rescue the defect of mfa1 expression as well as conjugation tube formation in response to pheromone induction in the rak1 mutant. Moreover, a solopathogenic rak1 mutant failed to respond to plant-derived stimuli, resulting in attenuated filamentation and pathogenicity. This could be partially rescued by constitutive expression of the b heterodimer. These data suggest that rak1 is a regulator of rop1 expression with additional roles after cell fusion.
在哺乳动物细胞中，RACK1 作为一种支架蛋白，在整合来自不同信号通路的输入方面发挥作用，并通过与核糖体的结合影响翻译。玉米黑粉菌含有一种名为 Rak1 的七 WD40 重复基序蛋白，与 RACK1 有 68%的同源性，与酿酒酵母的 Asc1p 有 51%的同源性。asc1 突变体可以通过引入玉米黑粉菌的 rak1 来互补。rak1 的缺失影响细胞生长、细胞壁完整性，并特异性地减弱细胞融合。后一缺陷是由于编码交配型（mfa）和交配型受体基因调节剂 prf1 的表达减少所致。Rak1 与多种核糖体蛋白相互作用，微阵列分析显示，rak1 的缺失导致 rop1 的表达严重减少，rop1 是 prf1 的转录激活因子。rop1 的组成型表达可以挽救 rak1 突变体中 mfa1 表达的缺陷以及交配诱导的交配管形成缺陷。此外，单突变体 rak1 不能对植物来源的刺激物作出反应，导致菌丝体减弱和致病性降低。这可以通过组成型表达 b 异二聚体部分挽救。这些数据表明，rak1 是 rop1 表达的调节剂，在细胞融合后具有额外的作用。
