Antigen 43, the major phase-variable protein of the Escherichia coli outer membrane, can exist as a family of proteins encoded by multiple alleles.
agn43 encodes a major phase-variable outer-membrane protein, antigen 43 (Ag43), involved in autoaggregation of Escherichia coli cells. The gene is present in single copy on the chromosome of E. coli K-12. In contrast, Southern hybridization and gene inactivation studies demonstrate that control producer strain E. coli ML308-225 possesses duplicate copies of agn43 (agn43A and agn43B). Construction and analyses of single and double knockout mutants clearly show that both alleles are capable of expressing antigen in a phase-variable manner, with observed differences in the ON<-->OFF switch frequencies appearing to favour expression of Ag43B under conditions of normal laboratory growth. Comparative analysis of agn43A and agn43B gene sequences revealed 98% identity at the nucleotide and predicted protein levels, with differences in the protein sequence of the surface-expressed alpha(43) subunit altering the surface probability of one of the predicted epitopes. Analysis of a panel of enteropathogenic E. coli strains by Southern hybridization using agn43-specific gene probes provided strong evidence for the presence of varying numbers of agn43 alleles within clinical isolates. Taken together, the results indicate the presence of a family of distinct Ag43 proteins encoded by multiple chromosomal alleles.
Roche
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Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin 2, Ireland.
McFadden
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J
Owen
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D018829:Adhesins, Bacterial; D018830:Adhesins, Escherichia coli; D000483:Alleles; D000940:Antigenic Variation; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D015153:Blotting, Western; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000276:immunology*; D029968:Escherichia coli Proteins; D020440:Gene Duplication; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D017422:Sequence Analysis, DNA
D018829:Adhesins, Bacterial; D018830:Adhesins, Escherichia coli; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; C118376:antigen 43, E coli