Institute of Molecular Genetics, Russian Academy of Sciences, Moscow 123182, Russia.
J Biol Chem. 2012 Jul 6;287(28):23779-89. doi: 10.1074/jbc.M112.363242. Epub 2012 May 17.
RNA polymerase (RNAP) from thermophilic Thermus aquaticus is characterized by higher temperature of promoter opening, lower promoter complex stability, and higher promoter escape efficiency than RNAP from mesophilic Escherichia coli. We demonstrate that these differences are in part explained by differences in the structures of the N-terminal regions 1.1 and 1.2 of the E. coli σ(70) and T. aquaticus σ(A) subunits. In particular, region 1.1 and, to a lesser extent, region 1.2 of the E. coli σ(70) subunit determine higher promoter complex stability of E. coli RNAP. On the other hand, nonconserved amino acid substitutions in region 1.2, but not region 1.1, contribute to the differences in promoter opening between E. coli and T. aquaticus RNAPs, likely through affecting the σ subunit contacts with DNA nucleotides downstream of the -10 element. At the same time, substitutions in σ regions 1.1 and 1.2 do not affect promoter escape by E. coli and T. aquaticus RNAPs. Thus, evolutionary substitutions in various regions of the σ subunit modulate different steps of the open promoter complex formation pathway, with regions 1.1 and 1.2 affecting promoter complex stability and region 1.2 involved in DNA melting during initiation.
RNA 聚合酶（RNAP）来自嗜热的水生栖热菌，其启动子开放的温度更高、启动子复合物的稳定性更低、启动子逃逸效率更高，而 RNAP 来自中温的大肠杆菌。我们证明这些差异部分是由大肠杆菌σ（70）和水生栖热菌σ（A）亚基的 N 端区域 1.1 和 1.2 的结构差异造成的。特别是大肠杆菌σ（70）亚基的区域 1.1 和在较小程度上区域 1.2 决定了大肠杆菌 RNAP 更高的启动子复合物稳定性。另一方面，区域 1.2 中的非保守氨基酸取代，而不是区域 1.1，导致了大肠杆菌和水生栖热菌 RNAP 之间启动子开放的差异，可能通过影响σ亚基与-10 元件下游 DNA 核苷酸的接触。同时，σ 区域 1.1 和 1.2 中的取代不影响大肠杆菌和水生栖热菌 RNAP 的启动子逃逸。因此，σ 亚基各个区域的进化取代调节了开放启动子复合物形成途径的不同步骤，区域 1.1 和 1.2 影响启动子复合物的稳定性，区域 1.2 参与启动过程中的 DNA 解链。
