Signaling mechanisms for activation of extracytoplasmic function (ECF) sigma factors

A variety of mechanisms are used to signal extracytoplasmic conditions to the cytoplasm. These mechanisms activate extracytoplasmic function (ECF) sigma factors which recruit RNA-polymerase to specific genes in order to express appropriate proteins in response to the changing environment. The two best understood ECF signaling pathways regulate σE-mediated expression of periplasmic stress response genes in Escherichia coli and FecI-mediated expression of iron–citrate transport genes in E. coli. Homologues from other Gram-negative bacteria suggest that these two signaling mechanisms and variations on these mechanisms may be the general schemes by which ECF sigma factors are regulated in Gram-negative bacteria.