Kazmierczak Mark J, Wiedmann Martin, Boor Kathryn J
Department of Food Science, Cornell University, 414 Stocking Hall, Ithaca, New York 14853, USA.
Microbiol Mol Biol Rev. 2005 Dec;69(4):527-43. doi: 10.1128/MMBR.69.4.527-543.2005.
Sigma factors provide promoter recognition specificity to RNA polymerase holoenzyme, contribute to DNA strand separation, and then dissociate from the core enzyme following transcription initiation. As the regulon of a single sigma factor can be composed of hundreds of genes, sigma factors can provide effective mechanisms for simultaneously regulating expression of large numbers of prokaryotic genes. One newly emerging field is identification of the specific roles of alternative sigma factors in regulating expression of virulence genes and virulence-associated genes in bacterial pathogens. Virulence genes encode proteins whose functions are essential for the bacterium to effectively establish an infection in a host organism. In contrast, virulence-associated genes can contribute to bacterial survival in the environment and therefore may enhance the capacity of the bacterium to spread to new individuals or to survive passage through a host organism. As alternative sigma factors have been shown to regulate expression of both virulence and virulence-associated genes, these proteins can contribute both directly and indirectly to bacterial virulence. Sigma factors are classified into two structurally unrelated families, the sigma70 and the sigma54 families. The sigma70 family includes primary sigma factors (e.g., Bacillus subtilis sigma(A)) as well as related alternative sigma factors; sigma54 forms a distinct subfamily of sigma factors referred to as sigma(N) in almost all species for which these proteins have been characterized to date. We present several examples of alternative sigma factors that have been shown to contribute to virulence in at least one organism. For each sigma factor, when applicable, examples are drawn from multiple species.
σ因子赋予RNA聚合酶全酶启动子识别特异性，有助于DNA链分离，然后在转录起始后与核心酶解离。由于单个σ因子的调控子可由数百个基因组成，σ因子可为同时调控大量原核基因的表达提供有效机制。一个新兴领域是鉴定替代σ因子在调节细菌病原体毒力基因和毒力相关基因表达中的特定作用。毒力基因编码的蛋白质功能对于细菌在宿主生物体中有效建立感染至关重要。相比之下，毒力相关基因可有助于细菌在环境中生存，因此可能增强细菌传播到新个体或在通过宿主生物体后存活的能力。由于替代σ因子已被证明可调节毒力基因和毒力相关基因的表达，这些蛋白质可直接和间接促进细菌毒力。σ因子分为两个结构不相关的家族，即σ70家族和σ54家族。σ70家族包括主要的σ因子（如枯草芽孢杆菌的σ(A)）以及相关的替代σ因子；在几乎所有已对这些蛋白质进行表征的物种中，σ54形成了一个独特的σ因子亚家族，称为σ(N)。我们给出了几个替代σ因子的例子，这些例子已被证明至少在一种生物体中对毒力有贡献。对于每个σ因子，如有适用情况，例子取自多个物种。
