Fig. 6. A schematic model of cell division in S. mutans.

1. Cell division is initiated at mid-cell by recruitment and alignment of the FtsZ-ring with the equatorial ring. Alignment of the FtsZ-ring is guided by MapZ which binds to peptidoglycan carrying immature SCCs. The AtlA Bsp domain targets the autolysin to the cell poles and equatorial ring populated by immature SCCs. 2. Cell division machinery assembled at mid-cell initiates synthesis of septal and lateral walls. Concomitantly with this process, the equatorial ring is split in the middle presumably under turgor pressure and due to AtlA action. Splitting of the septal wall and synthesis of the lateral wall leads to migration of new equatorial rings apart. The MapZ-rings follow the equatorial ring. The Bsp and catalytic domains of AtlA target the autolysin to parental septum to cleave the septal wall. 3. The equatorial rings approach the equator of new daughter cells. MapZ guides alignment of FtsZ with new equatorial rings. 4. Cell division machinery synthesizes the polar septal wall decorated with immature SCCs. The Bsp domain of AtlA mediates recruitment of the autolysin to newly forming poles to separate the daughter cells. Cell walls decorated with mature and immature SCCs are shown in gray and blue, respectively. Purple circles indicate AtlA. FtsZ- and MapZ-rings are shown in red and orange colors, respectively.