|σ 32||RpoH||Heat Shock σ Factor.|
|σ E||RpoE||Extracytoplasmic σ factor.|
|σ 54||RpoN||Nitrogen responsive σ factor.|
|σ S||RpoS||Stationary phase σ factor.|
The σ factor is a prokaryotic initiation factor that binds RNAP and promotes attachment to DNA promoter sites in response to significant environmental changes. For example, specific σ factors respond to hot or cold environments. σ factors promote transcription of genes which are not transcribed under normal conditions; these genes encode proteins to aid survival of environmental stress. In technical terms, developmental responses involve transcription of genes encoding specialized σ factors. Region 1 regulates interaction with DNA. Region 2 binds RNAP and binds to the -10 promoter site. Region 4 binds to the -35 promoter site.