Mechanisms of Action of Non-Canonical ECF Sigma Factors Marcos Torres, Francisco Javier Moraleda Muñoz, Aurelio Contreras Moreno, Francisco Javier Muñoz Dorado, José Pérez Torres, Juana ECF sigma factor Transcriptional regulation Stress response Extracytoplasmic function (ECF) sigma factors are subunits of the RNA polymerase specialized in activating the transcription of a subset of genes responding to a specific environmental condition. The signal-transduction pathways where they participate can be activated by diverse mechanisms. The most common mechanism involves the action of a membrane-bound anti-sigma factor, which sequesters the ECF sigma factor, and releases it after the stimulus is sensed. However, despite most of these systems following this canonical regulation, there are many ECF sigma factors exhibiting a non-canonical regulatory mechanism. In this review, we aim to provide an updated and comprehensive view of the different activation mechanisms known for non-canonical ECF sigma factors, detailing their inclusion to the different phylogenetic groups and describing the mechanisms of regulation of some of their representative members such as EcfG from Rhodobacter sphaeroides, showing a partner-switch mechanism; EcfP from Vibrio parahaemolyticus, with a phosphorylation-dependent mechanism; or CorE from Myxococcus xanthus, regulated by a metal-sensing C-terminal extension. 2022-04-20T09:54:27Z 2022-04-20T09:54:27Z 2022-03-25 info:eu-repo/semantics/article Marcos-Torres, F.J.; Moraleda-Muñoz, A.; Contreras-Moreno, F.J.; Muñoz-Dorado, J.; Pérez, J. Mechanisms of Action of Non-Canonical ECF Sigma Factors. Int. J. Mol. Sci. 2022, 23, 3601. [https://doi.org/10.3390/ijms23073601] http://hdl.handle.net/10481/74391 10.3390/ijms23073601 eng http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España MDPI