Besides the “housekeeping” sigma factor 70, other sigma factors in E.coli include: 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.