Voit R, Hoffmann M, Grummt I
Division of Molecular Biology of the Cell II, German Cancer Research Center, D-69120 Heidelberg, Germany.
EMBO J. 1999 Apr 1;18(7):1891-9. doi: 10.1093/emboj/18.7.1891.
Transcription of rRNA genes by RNA polymerase I increases following serum stimulation of quiescent NIH 3T3 fibroblasts. To elucidate the mechanism underlying transcriptional activation during progression through the G1 phase of the cell cycle, we have analyzed the activity and phosphorylation pattern of the nucleolar transcription factor upstream binding factor (UBF). Using a combination of tryptic phosphopeptide mapping and site-directed mutagenesis, we have identified Ser484 as a direct target for cyclin-dependent kinase 4 (cdk4)-cyclin D1- and cdk2-cyclin E-directed phosphorylation. Mutation of Ser484 impairs rDNA transcription in vivo and in vitro. The data demonstrate that UBF is regulated in a cell cycle-dependent manner and suggest a link between G1 cdks-cyclins, UBF phosphorylation and rDNA transcription activation.
静止的NIH 3T3成纤维细胞经血清刺激后，RNA聚合酶I对rRNA基因的转录增加。为阐明细胞周期G1期进程中转录激活的潜在机制，我们分析了核仁转录因子上游结合因子（UBF）的活性和磷酸化模式。通过胰蛋白酶磷酸肽图谱分析和定点诱变相结合的方法，我们确定Ser484是细胞周期蛋白依赖性激酶4（cdk4）-细胞周期蛋白D1以及cdk2-细胞周期蛋白E介导的磷酸化的直接靶点。Ser484突变会损害体内和体外的rDNA转录。数据表明UBF以细胞周期依赖性方式受到调控，并提示G1期细胞周期蛋白依赖性激酶-细胞周期蛋白、UBF磷酸化与rDNA转录激活之间存在联系。
