Editing Sigma factor (section)

==Specialized sigma factors==
Different sigma factors are utilized 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 ''[[Escherichia coli|E. coli]]'':
*[[RpoD|σ<sup>70</sup>(RpoD)]] – σ<sup>A</sup> – the '''"housekeeping" sigma factor''' or also called as '''primary sigma factor''' (Group 1), transcribes most genes in growing cells.  Every cell has a "housekeeping" sigma factor that keeps essential genes and pathways operating.<ref name="gross"/> In the case of ''E. coli'' and other gram-negative rod-shaped bacteria, the "housekeeping" sigma factor is σ<sup>70</sup>.<ref name="gross"/>  Genes recognized by σ<sup>70</sup> all contain similar promoter [[consensus sequence]]s consisting of two parts.<ref name="gross"/>  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).
*[[FecI|σ<sup>19</sup> (FecI)]] – the ferric citrate sigma factor, regulates the ''fec'' gene for iron transport and metabolism
*[[RpoE|σ<sup>24</sup> (RpoE)]] – extreme heat stress response and the extracellular proteins sigma factor
*[[RpoF|σ<sup>28</sup> (RpoF/FliA)]] – the [[Flagellum|flagellar]] synthesis and [[chemotaxis]] sigma factor
*σ<sup>32</sup> (RpoH) – the [[Heat shock response|heat shock]] sigma factor, it is turned on when the bacteria are exposed to heat. Due to the higher expression, the factor will bind with a high probability to the polymerase-core-enzyme. Doing so, other heatshock proteins are expressed, which enable the cell to survive higher temperatures. Some of the enzymes that are expressed upon activation of σ<sup>32</sup> are [[Chaperone (protein)|chaperones]], [[proteases]] and DNA-repair enzymes.
*[[RpoS|σ<sup>38</sup> (RpoS)]] – the starvation/stationary phase sigma factor
*[[RpoN|σ<sup>54</sup> (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.