Specialized Sigma Factors
Different sigma factors are activated under different environmental conditions. These specialized sigma factors bind the promoters of genes appropriate to the environmental conditions, increasing the transcription of those genes.
Sigma factors in E. coli:
- σ70(RpoD) - σA - the "housekeeping" sigma factor or also called as primary sigma factor, transcribes most genes in growing cells. Every cell has a “housekeeping” sigma factor that keeps essential genes and pathways operating. In the case of E. coli and other gram-negative rod-shaped bacteria, the "housekeeping" sigma factor is σ70. Genes recognized by σ70 all contain similar promoter consensus sequences consisting of two parts. Relative to the DNA base corresponding to the start of the RNA transcript, the consensus promoter sequences are characteristically centered at 10 and 35 nucleotides before the start of transcription (–10 and –35).
- σ19 (FecI) - the ferric citrate sigma factor, regulates the fec gene for iron transport
- σ24 (RpoE) - the extracytoplasmic/extreme heat stress sigma factor
- σ28 (RpoF) - the flagellar sigma factor
- σ32 (RpoH) - the heat shock sigma factor, it is turned on when exposed to heat
- σ38 (RpoS) - the starvation/stationary phase sigma factor
- σ54 (RpoN) - the nitrogen-limitation sigma factor
There are also anti-sigma factors that inhibit the function of sigma factors and anti-anti-sigma factors that restore sigma factor function.
Read more about this topic: Sigma Factor
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