Ryu S, Zhou S, Ladurner A G, Tjian R
Howard Hughes Medical Institute, University of California at Berkeley, Molecular and Cell Biology, 94720-3204, USA.
Nature. 1999 Feb 4;397(6718):446-50. doi: 10.1038/17141.
Activation of gene transcription in metazoans is a multistep process that is triggered by factors that recognize transcriptional enhancer sites in DNA. These factors work with co-activators to direct transcriptional initiation by the RNA polymerase II apparatus. One class of co-activator, the TAF(II) subunits of transcription factor TFIID, can serve as targets of activators and as proteins that recognize core promoter sequences necessary for transcription initiation. Transcriptional activation by enhancer-binding factors such as Sp1 requires TFIID, but the identity of other necessary cofactors has remained unknown. Here we describe a new human factor, CRSP, that is required together with the TAF(II)s for transcriptional activation by Sp1. Purification of CRSP identifies a complex of approximate relative molecular mass 700,000 (M(r) approximately 700K) that contains nine subunits with M(r) values ranging from 33K to 200K. Cloning of genes encoding CRSP subunits reveals that CRSP33 is a homologue of the yeast mediator subunit Med7, whereas CRSP150 contains a domain conserved in yeast mediator subunit Rgr1. CRSP p200 is identical to the nuclear hormone-receptor co-activator subunit TRIP2/PBP. CRSPs 34, 77 and 130 are new proteins, but the amino terminus of CRSP70 is homologous to elongation factor TFIIS. Immunodepletion studies confirm that these subunits have an essential cofactor function. The presence of common subunits in distinct cofactor complexes suggests a combinatorial mechanism of co-activator assembly during transcriptional activation.
后生动物中基因转录的激活是一个多步骤过程，由识别DNA中转录增强子位点的因子触发。这些因子与共激活因子协同作用，通过RNA聚合酶II装置指导转录起始。一类共激活因子，即转录因子TFIID的TAF(II)亚基，可作为激活因子的靶标以及识别转录起始所需核心启动子序列的蛋白质。诸如Sp1等增强子结合因子的转录激活需要TFIID，但其他必要辅助因子的身份仍不清楚。在这里，我们描述了一种新的人类因子CRSP，它与TAF(II)一起是Sp1转录激活所必需的。CRSP的纯化鉴定出一个相对分子质量约为700,000（M(r)约为700K）的复合物，该复合物包含九个亚基，其M(r)值范围为33K至200K。编码CRSP亚基的基因克隆表明，CRSP33是酵母中介体亚基Med7的同源物，而CRSP150包含在酵母中介体亚基Rgr1中保守的结构域。CRSP p200与核激素受体共激活因子亚基TRIP2/PBP相同。CRSPs 34、77和130是新蛋白质，但CRSP70的氨基末端与延伸因子TFIIS同源。免疫去除研究证实这些亚基具有必需的辅助因子功能。不同辅助因子复合物中存在共同亚基表明转录激活过程中共激活因子组装的组合机制。
