Oar, a 115-kilodalton membrane protein required for development of Myxococcus xanthus

Myxococcus xanthus is a developmental gram-negative bacterium which forms multicellular fruiting bodies upon nutrient starvation. This bacterium was found to contain a 115-kDa membrane protein which separated with the inner membrane fraction by sucrose density gradient centrifugation. The gene for this protein was cloned, and its DNA sequence was determined. The deduced amino acid sequence consists of 1,061 residues. This protein contains a putative signal sequence and many short segments, found scattered throughout the entire protein, that have sequence similarities with OmpA, a major outer membrane protein of Escherichia coli. Thus, the gene was designated oar (OmpA-related protein). A second open reading frame was found 36 bases downstream of the oar termination codon. This open reading frame encodes a protein of 236 residues and contains a putative lipoprotein signal sequence. An aor disruption mutation (delta oar) showed no effect on vegetative growth but caused abnormal morphogenesis during development and reduced myxospore formation. When examined with a light microscope, delta oar cells were unable to aggregate on developmental agar, indicating that Oar is required for cellular adhesiveness during development.