Cogswell J P, Godlevski M M, Bonham M, Bisi J, Babiss L
Department of Molecular Genetics, Glaxo Research Institute, Research Triangle Park, North Carolina 27709, USA.
Mol Cell Biol. 1995 May;15(5):2782-90. doi: 10.1128/MCB.15.5.2782.
Progression through the somatic cell cycle requires the temporal regulation of cyclin gene expression and cyclin protein turnover. One of the best-characterized examples of this regulation is seen for the B-type cyclins. These cyclins and their catalytic component, cdc2, have been shown to mediate both the entry into and maintenance of mitosis. The cyclin B1 gene has been shown to be expressed between the late S and G2 phases of the cell cycle, while the protein is degraded specifically at interphase via ubiquitination. To understand the molecular basis for transcriptional regulation of the cyclin B1 gene, we cloned the human cyclin B1 gene promoter region. Using a chloramphenicol acetyltransferase reporter system and both stable and transient assays, we have shown that the cyclin B1 gene promoter (extending to -3800 bp relative to the cap site) can confer G2-enhanced promoter activity. Further analysis revealed that an upstream stimulatory factor (USF)-binding site and its cognate transcription factor(s) are critical for expression from the cyclin B1 promoter in cycling HeLa cells. Interestingly, USF DNA-binding activity appears to be regulated in a G2-specific fashion, supporting the idea that USF may play some role in cyclin B1 gene activation. These studies suggest an important link between USF and the cyclin B1 gene, which in part explains how maturation promoting factor complex formation is regulated.
体细胞周期的进程需要对细胞周期蛋白基因表达和细胞周期蛋白的蛋白质周转进行时间调控。这种调控最典型的例子之一是B型细胞周期蛋白。这些细胞周期蛋白及其催化成分cdc2已被证明介导有丝分裂的进入和维持。细胞周期蛋白B1基因已被证明在细胞周期的S期晚期和G2期之间表达，而该蛋白在间期通过泛素化被特异性降解。为了了解细胞周期蛋白B1基因转录调控的分子基础，我们克隆了人细胞周期蛋白B1基因的启动子区域。使用氯霉素乙酰转移酶报告系统以及稳定和瞬时分析，我们已经表明细胞周期蛋白B1基因启动子（相对于帽位点延伸至-3800 bp）可以赋予G2增强的启动子活性。进一步的分析表明，上游刺激因子（USF）结合位点及其同源转录因子对于循环HeLa细胞中细胞周期蛋白B1启动子的表达至关重要。有趣的是，USF的DNA结合活性似乎以G2特异性方式受到调控，这支持了USF可能在细胞周期蛋白B1基因激活中发挥某些作用的观点。这些研究表明USF与细胞周期蛋白B1基因之间存在重要联系，这部分解释了成熟促进因子复合物的形成是如何被调控的。
