Bacterial chromosome segregation is facilitated by the ParABS system. The ParB protein binds centromere-like parS sequences and forms nucleoprotein complexes. These nucleoprotein complexes are segregated by the dynamic ATPase ParA. In mycobacteria, ParA also interacts with the polar growth determinant DivIVA (Wag31). This interaction was earlier shown to facilitate the segregation of ParB complexes but also to affect cell extension. Here, we identify an additional partner of ParA in Mycobacterium smegmatis, named PapM. Using E. coli based analysis, we show that PapM likewise interacts with DivIVA and that the tripartite interaction of ParA-PapM-DivIVA is phosphorylation-dependent: ParA binding to DivIVA is diminished, while PapM binding is promoted upon phosphorylation of DivIVA. The presence of PapM enhances the dissociation of ParA from the DivIVA complex upon its phosphorylation. Studies of M. smegmatis mutant strains reveal that altered PapM levels influence chromosome segregation and cell length. The elimination of PapM affects ParA dynamics. Further, ParA and, to a lesser extent, PapM modulates the subcellular distribution of DivIVA. Altogether our studies show that the tripartite interplay between ParA-DivIVA and PapM controls the switch between cell division and cell elongation and in this way affects the mycobacterial cell cycle.
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