McCulloch V, Hardin P, Peng W, Ruppert J M, Lobo-Ruppert S M
Department of Medical Genetics, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
EMBO J. 2000 Aug 1;19(15):4134-43. doi: 10.1093/emboj/19.15.4134.
In yeast, a single form of TFIIIB is required for transcription of all RNA polymerase III (pol III) genes. It consists of three subunits: the TATA box-binding protein (TBP), a TFIIB-related factor, BRF, and B". Human TFIIIB is not as well defined and human pol III promoters differ in their requirements for this activity. A human homolog of yeast BRF was shown to be required for transcription at the gene-internal 5S and VA1 promoters. Whether or not it was also involved in transcription from the gene-external human U6 promoter was unclear. We have isolated cDNAs encoding alternatively spliced forms of human BRF that can complex with TBP. Using immunopurified complexes containing the cloned hBRFs, we show that while hBRF1 functions at the 5S, VA1, 7SL and EBER2 promoters, a different variant, hBRF2, is required at the human U6 promoter. Thus, pol III utilizes different TFIIIB complexes at structurally distinct promoters.
在酵母中,所有RNA聚合酶III(pol III)基因的转录都需要单一形式的TFIIIB。它由三个亚基组成:TATA框结合蛋白(TBP)、一个与TFIIB相关的因子BRF和B"。人TFIIIB的定义并不明确,人pol III启动子对这种活性的需求也有所不同。酵母BRF的人同源物已被证明是基因内部5S和VA1启动子转录所必需的。它是否也参与基因外部人U6启动子的转录尚不清楚。我们分离出了编码可与TBP形成复合物的人BRF可变剪接形式的cDNA。使用含有克隆的hBRFs的免疫纯化复合物,我们发现虽然hBRF1在5S、VA1、7SL和EBER2启动子处发挥作用,但人U6启动子需要一种不同的变体hBRF2。因此,pol III在结构不同的启动子处利用不同的TFIIIB复合物。