Phosphate Flow between Hybrid Histidine Kinases CheA3 and CheS3 Controls Rhodospirillum centenum Cyst Formation

Genomic and genetic analyses have demonstrated that many species contain multiple chemotaxis-like signal transduction cascades that likely control processes other than chemotaxis. The Che 3 signal transduction cascade from Rhodospirillum centenum is one such example that regulates development of dormant cysts. This Che-like cascade contains two hybrid response regulator-histidine kinases, CheA 3 and CheS 3 , and a single-domain response regulator CheY 3 . We demonstrate that cheS 3 is epistatic to cheA 3 and that only CheS 3 ∼P can phosphorylate CheY 3 . We further show that CheA 3 derepresses cyst formation by phosphorylating a CheS 3 receiver domain. These results demonstrate that the flow of phosphate as defined by the paradigm E. coli chemotaxis cascade does not necessarily hold true for non-chemotactic Che-like signal transduction cascades.