Ouhammouch Mohamed, Hausner Winfried, Geiduschek E Peter
Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0634, USA.
Mol Microbiol. 2009 Jan;71(1):123-31. doi: 10.1111/j.1365-2958.2008.06512.x. Epub 2008 Nov 4.
The TATA box binding protein (TBP) is the platform for assembly of archaeal and eukaryotic transcription preinitiation complexes. Ancestral gene duplication and fusion events have produced the saddle-shaped TBP molecule, with its two direct-repeat subdomains and pseudo-two-fold symmetry. Collectively, eukaryotic TBPs have diverged from their present-day archaeal counterparts, which remain highly symmetrical. The similarity of the N- and C-halves of archaeal TBPs is especially pronounced in the Methanococcales and Thermoplasmatales, including complete conservation of their N- and C-terminal stirrups; along with helix H'1, the C-terminal stirrup of TBP forms the main interface with TFB/TFIIB. Here, we show that, in stark contrast to its eukaryotic counterparts, multiple substitutions in the C-terminal stirrup of Methanocaldococcus jannaschii (Mja) TBP do not completely abrogate basal transcription. Using DNA affinity cleavage, we show that, by assembling TFB through its conserved N-terminal stirrup, Mja TBP is in effect ambidextrous with regard to basal transcription. In contrast, substitutions in either its N- or the C-terminal stirrup abrogate activated transcription in response to the Lrp-family transcriptional activator Ptr2.
TATA框结合蛋白（TBP）是古细菌和真核生物转录起始前复合物组装的平台。祖先基因的复制和融合事件产生了鞍形的TBP分子，它有两个直接重复亚结构域和假二重对称。总的来说，真核生物的TBP已经与其当今高度对称的古细菌对应物有所不同。古细菌TBP的N端和C端的相似性在甲烷球菌目和热原体目中尤为明显，包括它们的N端和C端马镫结构的完全保守；与螺旋H'1一起，TBP的C端马镫结构形成了与TFB/TFIIB的主要界面。在这里，我们表明，与真核生物对应物形成鲜明对比的是，詹氏甲烷球菌（Mja）TBP的C端马镫结构中的多个取代并不完全消除基础转录。通过DNA亲和切割，我们表明，通过其保守的N端马镫结构组装TFB，Mja TBP在基础转录方面实际上是双手通用的。相比之下，其N端或C端马镫结构中的取代会消除对Lrp家族转录激活因子Ptr2的激活转录反应。
