Nucleotide sequences of the genes regulating O-polysaccharide antigen chain length (rol) from Escherichia coli and Salmonella typhimurium: protein homology and functional complementation

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Abstract
In this article, we report on the nucleotide sequences of the rol genes of Escherichia coli O75 and Salmonella typhimurium LT2. The rol gene in E. coli was previously shown to encode a 36-kDa protein that regulates size distribution of the O-antigen moiety of lipopolysaccharide. The E. coli and S. typhimurium rol gene sequences consist of 978 and 984 nucleotides, respectively. The homology between the nucleotide sequences of these two genes was found to be 68.9%. Both the E. coli rol and S. typhimurium rol genes are transcribed counter to the histidine operon and code for deduced polypeptides of 325 and 327 amino acids, respectively. The S. typhimurium rol gene was previously identified to encode a protein of unknown function and to share a transcription termination region with his. The homology between these deduced polypeptide sequences was observed to be 72%. A complementation test was performed in which the S. typhimurium rol gene was placed in trans with an E. coli plasmid (pRAB3) which encodes the O75 rfb gene cluster and not rol. The protein expressed from the S. typhimurium rol gene was found to regulate the distribution of the O75 O polysaccharide on the lipopolysaccharide of the host strain, E. coli S phi 874. The mechanism of Rol action may be independent of O antigen subunit structure, and its presence may be conserved in members of the family Enterobacteriaceae and other gram-negative bacilli that express O polysaccharides on their surface membrane.