酵母PAP1与PHO85激酶复合物对YLR190w的磷酸化

酵母基因Pho85编码一个依赖于细胞周期蛋白 (cyclin)的蛋白激酶 (CDK) ,参与多种调控途径。PHO85功能的多效性归于其相关的细胞周期因子 ,现已经鉴定了 10个与PHO85相关的细胞周期因子 (PCL)。为了筛选PAP1 PHO85激酶复合物的特异底物 ,以PAP1为靶分子 ,利用酵母双杂交 (two hybrid)系统从酵母cDNA文库中克隆到一个与PAP1相互作用的蛋白质因子的基因 ,Ylr190w。Ylr190w编码 491个氨基酸的多肽链。体外翻译的YLR190w与纯化的融合蛋白GST PAP1可以被谷胱甘肽亲和柱共同吸附 ,这表明PAP1与YLR190w在体外也可以结合。用免疫沉淀获得的PAP1 PHO85复合物可以磷酸化在大肠杆菌中表达GST YLR190w ;并受到无机磷浓度影响 :高磷条件时磷酸化程度高 ,低磷条件时磷酸化程度低。它能与酵母细胞内YAF9结合 ,YAF9是人具有转录调控活性蛋白质因子AF9的酵母同源物。YLR190w与YAF9的相互作用受到磷条件影响 ,突变YLR190w蛋白S/TP位点的S和T后 ,它们的相互作用明显减弱 ,且不再受到磷条件影响

Phosphorylation of YLR190w by PAP1-PHO85 Kinase Complex

A yeast two-hybrid screening by using PAP1 was performed to identify targets for PAP1-PHO85 cyclin-CDK complex. N-terminal fragment of protein YLR190w, a yeast gene encoding a 491 amino acids peptide, was identified, and its coding region was amplified by PCR. The interaction of PAP1 and YLR190w was confirmed by both two-hybrid assay and GST pull-down assay in vitro. The PAP1-PHO85 kinase complex obtained from the immunoprecipitates could phosphorylate GST-YLR190w expressed in E.coli, and the phosphorylation of YLR190w was affected by the phosphate concentration, and the phosphorylation sites of YLR190w were Ser/Thr-Pro motif, as revealed by protein mutation assay. In another library screen, YAF9, a yeast homolog of human AF9, was isolated using the two-hybrid system with YLR190w as the bait. It was revealed that interaction of YLR190w and YAF9 was affected by phosphate concentration. When all Ser/Thr in Ser/Thr-Pro motif were mutated to Ala, the interaction of YLR190w (mutant) and YAF9 was weakened, and the effect of phosphate concentration was impaired. Ylr190w was not involved in the PHO system by the acid phosphatase activity assay. Deletion of Ylr190w was constructed by homologous recombination and the doubling time of Ylr190w mutant strain was longer than that of wild type.