Cytokinesis signals truncation of the PodJ polarity factor by a cell cycle-regulated protease.

We demonstrate that successive cleavage events involving regulated intramembrane proteolysis (Rip) occur as a function of time during the Caulobacter cell cycle. The proteolytic substrate PodJ(L) is a polar factor that recruits proteins required for polar organelle biogenesis to the correct cell pole at a defined time in the cell cycle. We have identified a periplasmic protease (PerP) that initiates the proteolytic sequence by truncating PodJ(L) to a form with altered activity (PodJ(S)). Expression of perP is regulated by a signal transduction system that activates cell type-specific transcription programs and conversion of PodJ(L) to PodJ(S) in response to the completion of cytokinesis. PodJ(S), sequestered to the progeny swarmer cell, is subsequently released from the polar membrane by the membrane metalloprotease MmpA for degradation during the swarmer-to-stalked cell transition. This sequence of proteolytic events contributes to the asymmetric localization of PodJ isoforms to the appropriate cell pole. Thus, temporal activation of the PerP protease and spatial restriction of the polar PodJ(L) substrate cooperatively control the cell cycle-dependent onset of Rip.