Scaffold-scaffold interactions regulate cell polarity in a bacterium

The localization of two biochemically distinct signaling hubs at opposite cell poles provides the foundation for asymmetric cell division in Caulobacter crescentus. Here we identify an interaction between the scaffolds PodJ and PopZ that regulates the assembly of the new cell pole signaling complex. Time-course imaging of a mCherry-sfGFP-PopZ fluorescent timer throughout the cell cycle revealed that existing PopZ resides at the old cell pole while newly translated PopZ accumulates at the new cell pole. Our studies suggest that interactions between PodJ and PopZ promotes the sequestration of older PopZ and robust accumulation of newl PopZ at the new cell pole. Elimination of the PodJ-PopZ interaction impacts PopZ client proteins, leading to chromosome segregation defects in one-third of cells. Additionally, this PopZ-PodJ interaction is crucial for anchoring PodJ and preventing PodJ extracellular loss at the old cell pole through unknown mechanism. Therefore, segregation of PopZ protein at the old pole and recruitment of newly translated PopZ at the new pole via the PodJ scaffold ensures stringent inheritance and maintenance of the polarity axis within dividing C. crescentus cells.