Septal localization of FtsQ, an essential cell division protein in Escherichia coli

Septation in Escherichia coli requires several gene products. One of these, FtsQ, is a simple bitopic membrane protein with a short cytoplasmic N term inus, a membrane-spanning segment, and a periplasmic domain. We have constr ucted a merodiploid strain that expresses both FtsQ and the fusion protein green fluorescent protein (GFP)-FtsQ from single-copy chromosomal genes. Th e gfp-ftsQ gene complements a null mutation in pse Fluorescence microscopy revealed that GFP-FtsQ localizes to the division site. Replacing the cytopl asmic and transmembrane domains of FtsQ with alternative membrane anchors d id not prevent the localization of the GFP fusion protein, while replacing the periplasmic domain did, suggesting that the periplasmic domain is neces sary and sufficient for septal targeting. GFP-FtsQ localization to the sept um depended on the cell division proteins FtsZ and FtsA, which are cytoplas mic, but not on FtsL and FtsI, which are bitopic membrane proteins with com paratively large periplasmic domains. In addition, the septal localization of ZipA apparently did not require functional FtsQ. Our results indicate th at FtsQ is an intermediate recruit to the division site.