MapZ marks the division sites and positions FtsZ rings in Streptococcus pneumoniae

A new mechanism is identified for correct placement of the division machinery in Streptococcus pneumoniae that relies on the novel factor MapZ to form ring structures at the cell equator; these structures move apart as the cell elongates, acting as permanent markers of division sites. MapZ guides cell-division protein FtsZ In many bacteria, the correct mid-cell placement of the cell division machinery —including the ring formed by the conserved tubulin homologue FtsZ — is controlled by the Min system, which prevents FtsZ polymerization at the cell poles. This system is absent in the pathogenic bacterium Streptococcus pneumoniae , however. Here Christophe Grangeasse and colleagues identify a placement mechanism that does operate in S. pneumonia . It depends on mid-cell anchored protein Z (MapZ) to form ring structures at the cell equator that separate as the cell elongates, acting as a permanent beacon for the division sites. MapZ interacts with FtsZ to position the Z-ring for division. In every living organism, cell division requires accurate identification of the division site and placement of the division machinery. In bacteria, this process is traditionally considered to begin with the polymerization of the highly conserved tubulin-like protein FtsZ into a ring that locates precisely at mid-cell 1 . Over the past decades, several systems have been reported to regulate the spatiotemporal assembly and placement of the FtsZ ring 2 , 3 , 4 , 5 . However, the human pathogen Streptococcus pneumoniae , in common with many other organisms, is devoid of these canonical systems and the mechanisms of positioning the division machinery remain unknown 4 , 6 . Here we characterize a novel factor that locates at the division site before FtsZ and guides septum positioning in pneumococcus. Mid-cell-anchored protein Z (MapZ) forms ring structures at the cell equator and moves apart as the cell elongates, therefore behaving as a permanent beacon of division sites. MapZ then positions the FtsZ ring through direct protein–protein interactions. MapZ-mediated control differs from previously described systems mostly on the basis of negative regulation of FtsZ assembly. Furthermore, MapZ is an endogenous target of the Ser/Thr kinase StkP, which was recently shown to have a central role in cytokinesis and morphogenesis of S. pneumoniae 7 , 8 , 9 . We show that both phosphorylated and non-phosphorylated forms of MapZ are required for proper Z-ring formation and dynamics. Altogeth