The 25‐kDa peptidoglycan‐associated outer‐membrane protein and most likely porin of
Vibrio choleraeis a major immunogenic species. It has been purified by ion‐exchange elution on hydroxyapatite followed by gel filtration on Bio‐Gel P150 both in the presence of sodium dodecyl sulfate. This protein, of greater than 90% purity as judged by Western blotting, has been used to raise antibodies in rabbits. The antisera were then used to screen V. choleraegene banks, constructed in Escherichia coliK12, and this has enabled us to isolate several colonies harbouring the cloned gene. The plasmids in these colonies have been designated pPM451, pPM455 and pPM472. These plasmids have a 5.3 × 103‐base BamHI fragment of V. choleraeDNA in common. Restriction endonuclease mapping of these plasmids has been performed and the protein identified both by Western blot analysis and in E. coliK12 minicells. The protein is not efficiently expressed in E. coliK12. It is proposed to use the name ompVto describe the structural gene, present in the cloned DNA, for this V. choleraeouter membrane protein.