In-phase oscillation of global regulons is orchestrated by a pole-specific organizer

Cell fate determination in the asymmetric bacterium Caulobacter crescentus (Caulobacter) is triggered by the localization of the developmental regulator SpmX to the old (stalked) cell pole during the G1-S transition. While SpmX is required to localize and activate the cell fate-determining kinase DivJ at the stalked pole in Caulobacter, it is also required for organelle (stalk) positioning in the cousin Asticaccaulis. We unearth the conserved s54-dependent transcriptional activator regulator TacA as global regulator in Caulobacter whose activation by phosphorylation is indirectly down-regulated by SpmX. Using a combination of forward genetics and cytological screening we uncover a previously uncharacterized and polarized component (SpmY) of the TacA phosphorylation control system, and we show that the SpmY function and localization is conserved. Thus, we demonstrate that SpmX organizes a site-specific, ancestral and multi-functional regulatory hub whose function includes the coordinated control of two co-oscillating global transcriptional regulators, CtrA and TacA. Overall design: Examination of 2 transcription factors occupancy in WT and two mutant backgrounds + assessment of synthetic lethal and viable genes in WT and one null-allele background