Kwon H, Green M R
Howard Hughes Medical Institute, University of Massachusetts Medical Center, Worcester 01605.
J Biol Chem. 1994 Dec 2;269(48):30140-6.
The accurate transcription of human rRNA genes by RNA polymerase I requires two transcription factors, upstream binding factor (UBF) and promoter selectivity factor (SL1). Human SL1 (hSL1) is a multisubunit complex, one of whose components is TATA box-binding protein (TBP). hSL1 binds to the core region of the rRNA promoter, but does so inefficiently in the absence of human UBF (hUBF). hUBF interacts with the upstream control element of the rRNA promoter and facilitates binding of hSL1. The molecular basis by which hUBF increases binding of hSL1 remains to be elucidated. In this report, we use an immobilized protein binding assay to identify and purify a 95-kDa TBP-binding polypeptide. Microsequence analysis reveals that the 95-kDa TBP-binding protein is hUBF. We show that hUBF is stably associated with TBP and is present in large TBP-containing complexes. Our results indicate that the cooperative binding of hUBF and hSL1 on the rRNA promoter is mediated by direct interaction between hUBF and TBP. We also provide evidence that hUBF associates with TFIID, a TBP-containing RNA polymerase II transcription factor.
RNA聚合酶I对人类rRNA基因的准确转录需要两种转录因子，即上游结合因子（UBF）和启动子选择性因子（SL1）。人类SL1（hSL1）是一种多亚基复合物，其成分之一是TATA盒结合蛋白（TBP）。hSL1与rRNA启动子的核心区域结合，但在没有人类UBF（hUBF）的情况下，这种结合效率很低。hUBF与rRNA启动子的上游控制元件相互作用，并促进hSL1的结合。hUBF增强hSL1结合的分子基础仍有待阐明。在本报告中，我们使用固定化蛋白结合测定法来鉴定和纯化一种95 kDa的TBP结合多肽。微序列分析表明，95 kDa的TBP结合蛋白是hUBF。我们发现hUBF与TBP稳定结合，并存在于含TBP的大型复合物中。我们的结果表明，hUBF和hSL1在rRNA启动子上的协同结合是由hUBF和TBP之间的直接相互作用介导的。我们还提供证据表明，hUBF与TFIID相关联，TFIID是一种含TBP的RNA聚合酶II转录因子。
