FIG 1.
(A) Current models of EcfG sigma factor regulation in S. meliloti, C. crescentus, and Sphingomonas sp. strain Fr1. Arrows and T lines stand for positive and negative regulations, respectively. Dotted lines indicate hypothetical regulations or regulations only revealed in mutant backgrounds whose relevance under wild-type conditions is not clear. In the absence of stress, the sigma factors (RpoE2/SigT/σEcfG) are kept inactive by interaction with anti-sigma factors (RsiA/NepR). Under stress or starvation conditions, anti-anti-sigma factors (RsiB/PhyR) are activated by phosphorylation and relieve sigma factor inhibition by interacting with the anti-sigma factors. The various actors controlling the phosphorylation status of anti-anti-sigma factors are indicated at the top. These models were drawn according to the literature (5, 18, 23, 24, 35, 36) and the present work. (B) Schematic representation of the S. meliloti chromosomal region encoding RpoE2 and its regulators RsiA1, RsiB1, and RsiC.