Baldus J M, Buckner C M, Moran C P
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Mol Microbiol. 1995 Jul;17(2):281-90. doi: 10.1111/j.1365-2958.1995.mmi_17020281.x.
The transcriptional regulator Spo0A activates transcription from two types of promoters. One type of promoter is used by RNA polymerase containing sigma A, whereas the other type is used by RNA polymerase containing sigma H. There are Spo0A-binding sites near the -35 region of both types of promoters. It has been reported that some transcriptional regulators that bind near the -35 regions of promoters directly interact with the sigma subunit of RNA polymerase. Therefore, we looked for evidence that Spo0A interacts with both sigma factors by searching for single amino acid substitutions in these factors that specifically prevent expression from Spo0A-dependent promoters, but that do not decrease activity of Spo0A-independent promoters. Two such amino acid substitutions were isolated in sigma A and one was isolated in sigma H. The amino acid substitutions in sigma A prevented expression from the Spo0A-activated promoters, spoIIG and spoIIE, but expression was not impaired from the Spo0A-independent, sigma A-dependent promoter tms or from the Spo0A-activated, sigma H-dependent promoter, spoIIA. The amino acid substitution in sigma H prevented expression from the spoIIA promoter but not from the Spo0A-independent promoter, citGp2, which is used by sigma H-RNA polymerase. All of these amino acid substitutions occur in the carboxyl terminus of the sigma factors. These amino acid substitutions may define the sites of contact between the sigma factors and Spo0A. The ability of response regulators such as Spo0A to interact with multiple sigma factors may increase the variety of responses made by bacteria using a limited number of transcription factors.
转录调节因子Spo0A可激活两种类型启动子的转录。一种类型的启动子由含σA的RNA聚合酶使用，而另一种类型则由含σH的RNA聚合酶使用。在这两种类型启动子的-35区域附近都存在Spo0A结合位点。据报道，一些在启动子-35区域附近结合的转录调节因子可直接与RNA聚合酶的σ亚基相互作用。因此，我们通过寻找这些因子中的单氨基酸替代来寻找Spo0A与这两种σ因子相互作用的证据，这些替代可特异性阻止Spo0A依赖性启动子的表达，但不会降低Spo0A非依赖性启动子的活性。在σA中分离到两个这样的氨基酸替代，在σH中分离到一个。σA中的氨基酸替代阻止了Spo0A激活的启动子spoIIG和spoIIE的表达，但Spo0A非依赖性、σA依赖性启动子tms或Spo0A激活的、σH依赖性启动子spoIIA的表达未受影响。σH中的氨基酸替代阻止了spoIIA启动子的表达，但未阻止σH-RNA聚合酶使用的Spo0A非依赖性启动子citGp2的表达。所有这些氨基酸替代都发生在σ因子的羧基末端。这些氨基酸替代可能确定了σ因子与Spo0A之间的接触位点。像Spo0A这样的应答调节因子与多种σ因子相互作用的能力，可能会增加细菌利用有限数量转录因子产生的应答多样性。
