list E. coli alternative sigma factors
RpoS, RpoH, RpoE, RpoN, RpoF, FecI
RpoS
starvation/stationary
RpoH
heat shock
RpoE
extracytoplasmic/extreme heat
RpoN
nitrogen limitation
RpoF
flagellar
FecI
ferric citrate
promoter for housekeeping genes
RpoD