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Chromosomal location and expression of the structural gene for major outer membrane protein Ia of Escherichia coli K-12 and of the homologous gene of Salmonella typhimurium

The gene determining the structure of a major outer membrane protein of Escherichia coli, protein Ia, has been located between serC and pyrD, at the min 21 region of the linkage map. This is based on the isolation and characterization of E. coli-Salmonella typhimurium intergeneric hybrids as well as analyses of a mutation (ompF2) affecting the formation of protein Ia. When the serC region of the S. typhimurium chromosome was transduced by phage P1 into E. coli, two classes of transductants were obtained; one produced protein Ia like the parental strain of E. coli, whereas the other produced not protein Ia but a pair of outer membrane proteins structurally related to 35K protein, one of the major outer membrane proteins of S. typhimurium. Furthermore, a strain of S. typhimurium harboring an F' plasmid which carries the ompF region of the E. coli chromosome was found to produce a protein indistinguishable from protein Ia, beside the outer membrane proteins characteristic to the parental Salmonella strain. These results suggest that the structural genes for protein Ia (E. coli) and for 35K protein (S. typhimurium) are homologous to each other and are located at the ompF region of the respective chromosome. The bearing of these findings on the genetic control of protein Ia formation is discussed.