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Cloning of the rfb gene cluster of a group C2 Salmonella strain: comparison with the rfb regions of groups B and D

We report the cloning and mapping of the entire rfb gene cluster of a group C2 Salmonella strain. Comparison with the rfb region of group B strain LT2 and group D strain Ty2 reveals an 11.8kb central region of limited similarity flanked by regions of high similarity. The genes from the central region confer a group C2 O‐antigen structure on a Salmonella LT2 partial delete strain. The significance of this region in relation to function and evolutionary origin is discussed. We also report evidence for the existence of an O‐antigen chain‐length determinant in Escherichia coli K12 and propose a model for a possible mechanism by which a preferred chain length is determined.