Metal-responsive RNA polymerase extracytoplasmic function (ECF) sigma factors

Mol Microbiol. 2019 Aug;112(2):385-398. doi: 10.1111/mmi.14328. Epub 2019 Jun 26.


In order to survive, bacteria must adapt to multiple fluctuations in their environment, including coping with changes in metal concentrations. Many metals are essential for viability, since they act as cofactors of indispensable enzymes. But on the other hand, they are potentially toxic because they generate reactive oxygen species or displace other metals from proteins, turning them inactive. This dual effect of metals forces cells to maintain homeostasis using a variety of systems to import and export them. These systems are usually inducible, and their expression is regulated by metal sensors and signal-transduction mechanisms, one of which is mediated by extracytoplasmic function (ECF) sigma factors. In this review, we have focused on the metal-responsive ECF sigma factors, several of which are activated by iron depletion (FecI, FpvI and PvdS), while others are activated by excess of metals such as nickel and cobalt (CnrH), copper (CarQ and CorE) or cadmium and zinc (CorE2). We focus particularly on their physiological roles, mechanisms of action and signal transduction pathways.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Bacteria / enzymology
  • Bacteria / genetics
  • Bacteria / metabolism*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • DNA-Directed RNA Polymerases / genetics
  • DNA-Directed RNA Polymerases / metabolism*
  • Gene Expression Regulation, Bacterial
  • Metals / metabolism*
  • Sigma Factor / genetics
  • Sigma Factor / metabolism*


  • Bacterial Proteins
  • Metals
  • Sigma Factor
  • DNA-Directed RNA Polymerases