SK NmpU, RR-SK NmpS, and RR NmpR are in a single signaling pathway.

Epistasis analysis demonstrates these signaling proteins are in a shared pathway. Mutations in various strains were constructed as depicted and motility assayed as before. Note especially that deletion of nmpR or nmpS is epistatic to a deleted or non-functional nmpU (B and D); that suppressor mutations in nmpR arose in the NmpUQ283Stop ΔnmpS strain (B and Fig 4); and that deletion of nmpU is sufficient to restore motility in the ΔpilR parental strain (D). As before, over-expression of a phosphomimetic (D54E) NmpR is necessary to restore motility of a ΔnmpR strain (C). The motility image of the parental NmpRV87E strain (A) is a representative image reproduced from Fig 3A.