cir, a gene conferring resistance to colicin I maps between mgl and fpk on the Escherichia coli chromosome.

With the help of the tetracycline resistance transposon Tn10 in and around the mgl genes the gene cir was mapped. cir is 80% cotransducible with mgl by P1 transduction. The sequence of the surrounding markers in clockwise order was established as: cdd fpk cir mgl gyrA. The direction of transcription in cir was determined as clockwise on the Escherichia coli chromosome. The gene product of cir, an outer membrane receptor for colicin I, is not part of the mgl operon. It is not regulated by D-fucose, the inducer of the mgl system and mutants defective in cir are unimpaired in the uptake of substrates of the mgl-dependent transport system.