ArcB is a membrane protein activated by anoxia, perhaps by a reduced form of an electron carrier. The model postulates that the activated form of ArcB becomes phosphorylated and then phosphorylates ArcA, which then becomes a repressor of aerobically expressed enzymes and inducer of cytochrome d oxidase.
Heavy solid arrows indicate forward phosphotransfer reactions leading to formation of ArcA-P. Hatched arrows indicate the reverse phosphotransfer reactions leading to signal decay (1). Arrows with crosses indicate phosphotransfer reactions not substantiated by Kwon's study (5).
The results from the Kwon's study in E.coli, based on single-copy arcB alleles, suggest that the sole route of phosphotransfer from ArcB to ArcA is by a relay involving His292, Asp576, and His717 of the sensor kinase . In particular, there is no evidence for direct phosphoryl group transfer from His292 to ArcA or for the phosphorylation of ArcA by an unknown kinase via the H2 domain of ArcB. Their results indicate that the signal transmission occurs solely by His-Asp-His-Asp phosphorelay.
* This figure was modified from Kwon, O (5).