PMID:11160810
| Citation |
Roche, A, McFadden, J and Owen, P (2001) Antigen 43, the major phase-variable protein of the Escherichia coli outer membrane, can exist as a family of proteins encoded by multiple alleles. Microbiology (Reading, Engl.) 147:161-9 |
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| Abstract |
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. |
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| Keywords |
Adhesins, Bacterial; Alleles; Antigenic Variation; Antigens, Bacterial; Bacterial Outer Membrane Proteins/genetics; Bacterial Outer Membrane Proteins/immunology; Bacterial Outer Membrane Proteins/metabolism; Blotting, Western; Escherichia coli/genetics; Escherichia coli/growth & development; Escherichia coli/immunology; Escherichia coli Proteins; Gene Duplication; Humans; Molecular Sequence Data; Mutation; Sequence Analysis, DNA |
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