Kim S, Na J G, Hampsey M, Reinberg D
Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway 08854-5635, USA.
Proc Natl Acad Sci U S A. 1997 Feb 4;94(3):820-5. doi: 10.1073/pnas.94.3.820.
A general repressor extensively studied in vitro is the human Dr1/DRAP1 heterodimeric complex. To elucidate the function of Dr1 and DRAP1 in vivo, the yeast Saccharomyces cerevisiae Dr1/DRAP1 repressor complex was identified. The repressor complex is encoded by two essential genes, designated YDR1 and BUR6. The inviability associated with deletion of the yeast genes can be overcome by expressing the human genes. However, the human corepressor DRAP1 functions in yeast only when human Dr1 is coexpressed. The yDr1/Bur6 complex represses transcription in vitro in a reconstituted RNA polymerase II transcription system. Repression of transcription could be overcome by increasing the concentration of TATA-element binding protein (TBP). Consistent with the in vitro results, overexpression of YDR1 in vivo resulted in decreased mRNA accumulation. Furthermore, YDR1 overexpression impaired cell growth, an effect that could be rescued by overexpression of TBP. In agreement with our previous studies in vitro, we found that overexpression of Dr1 in vivo also affected the accumulation of RNA polymerase III transcripts, but not of RNA polymerase I transcripts. Our results demonstrate that Dr1 functions as a repressor of transcription in vivo and, moreover, directly targets TBP, a global regulator of transcription.
在体外被广泛研究的一种通用阻遏物是人类Dr1/DRAP1异二聚体复合物。为了阐明Dr1和DRAP1在体内的功能，鉴定了酿酒酵母Dr1/DRAP1阻遏物复合物。该阻遏物复合物由两个必需基因编码，分别命名为YDR1和BUR6。通过表达人类基因可以克服与酵母基因缺失相关的致死性。然而，人类共阻遏物DRAP1仅在共表达人类Dr1时才在酵母中发挥作用。yDr1/Bur6复合物在体外重构的RNA聚合酶II转录系统中抑制转录。增加TATA元件结合蛋白（TBP）的浓度可以克服转录抑制。与体外结果一致，体内YDR1的过表达导致mRNA积累减少。此外，YDR1的过表达损害细胞生长，而TBP的过表达可以挽救这种效应。与我们之前的体外研究一致，我们发现体内Dr1的过表达也影响RNA聚合酶III转录本的积累，但不影响RNA聚合酶I转录本的积累。我们的结果表明，Dr1在体内作为转录阻遏物发挥作用，而且直接靶向TBP，一种转录的全局调节因子。
