Two localization motifs mediate polar residence of FrzS during cell movement and reversals of Myxococcus xanthus.

Myxococcus xanthus utilizes two motility systems for surface locomotion: A-motility and S-motility. S-motility is mediated by extension and retraction of type IV pili. Cells exhibiting S-motility periodically reverse by switching the assembly of type IV pili from the old leading pole to the new leading pole. These cellular reversals involve regulated pole-to-pole oscillations of the FrzS protein. We constructed and characterized in-frame deletion mutations in several FrzS domains to determine their roles in protein localization. We found that FrzS has distinct domains required for residence at the leading cell pole, pole-to-pole transport and lagging cell pole. Our results are consistent with a model whereby S-motility reversals are mediated by a protein translocation system that delivers motility proteins such as FrzS from the leading cell pole to the lagging cell pole.