Dombroski A J
Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, Houston, Texas 77030, USA.
J Biol Chem. 1997 Feb 7;272(6):3487-94.
Promoter recognition by RNA polymerase depends upon its ability to bind to specific DNA sequences. The sigma (sigma) subunit provides selectivity for transcription initiation by interacting with the -10 and -35 elements of promoter DNA. Suppressor mutations in sigma factor that compensate for specific "down" substitutions in the promoter have demonstrated that sigma factor recognizes certain base pairs of the promoter. Since these suppressors were only identified for changes at the -12 and -11 positions of the -10 element (TATAAT), the role of the other base pairs of this region in specifying recognition by sigma factor remained unclear. Using a partial polypeptide of sigma70 carrying regions 2-4, this report shows that the first three positions of the -10 element (-12, -11, -10) are important for sigma factor alone to recognize and bind to duplex DNA. The sigma polypeptide also binds to an "extended -10" promoter, even without a -35 element. A mismatch bubble from -10 to +3 is bound regardless of the sequence within the bubble, or the presence or absence of a -35 element. Unexpectedly, binding to a mismatch bubble that lacks a -35 hexamer is sensitive to the identity of the -11 position, but not the -12 position.
RNA聚合酶对启动子的识别取决于其与特定DNA序列结合的能力。σ亚基通过与启动子DNA的-10和-35元件相互作用，为转录起始提供选择性。σ因子中的抑制突变可补偿启动子中特定的“下调”取代，这表明σ因子可识别启动子的某些碱基对。由于这些抑制子仅在-10元件（TATAAT）的-12和-11位置的变化中被鉴定出来，该区域其他碱基对在指定σ因子识别中的作用仍不清楚。本报告使用携带2-4区的σ70部分多肽，表明-10元件的前三个位置（-12、-11、-10）对于σ因子单独识别和结合双链DNA很重要。即使没有-35元件，σ多肽也能与“扩展-10”启动子结合。无论气泡内的序列如何，也无论是否存在-35元件，从-10到+3的错配气泡都会被结合。出乎意料的是，与缺乏-35六聚体的错配气泡结合对-11位置的身份敏感，但对-12位置不敏感。
