Required for the in vivo function of penicillin-binding protein 2a (PBP2a), which is involved in the biosynthesis of cross-linked peptidoglycan (PG) of the cell wall. Interacts with class A penicillin-binding proteins PBP1a and PBP2a. Localizes to sites of new peptidoglycan (PG) synthesis at midcell independently of PBP2a. C-terminal transmembrane domain is sufficient for its midcell localization, but not for the full function. Phosphorylation by StkP is required for its ability to promote PBP2a function. Synthetically lethal with PBP1a. Deletion of this gene with concomitant depletion of PBP1a leads to progressive reduction in cell size before ultimate lysis. Cell wall synthesis is also dramatically reduced in these cells. On the other hand, cells lacking this gene are unaffected by the depletion of PBP2a.