AN O-ANTIGEN PROCESSING FUNCTION FOR WZX (RFBX) - A PROMISING CANDIDATE FOR O-UNIT FLIPPASE

O antigen is the major cell surface antigen of gram-negative bacteria, and the genes responsible for its synthesis are located in a single g ene cluster. The wzx (rbfX) gene, which is characteristic of the major class of O-antigen gene clusters, encodes a hydrophobic protein with 12 potential transmembrane segments. We demonstrate that a ww mutant a ccumulates undecaprenol pyrophosphate-linked O units which appear to b e on the cytoplasmic side of the cytoplasmic membrane, suggesting that the wzx gene encodes a flippase for O-unit translocation across that membrane.