Abstract
Three multiply colicin-tolerant mutants in E. coli K-12 from the TolIV, TolXIV and TolXV phenotypic groups, all lacking or having only trace amounts of protein 1, a major outer-membrane protein, were mapped by Hfr crosses, and the position on the chromosome was confirmed by cotransduction with nearby markers. The mutations were located near malQP in the 74 min region of the E. coli chromosome. This locus is designated ompB, and analysis of data from two 3-point crosses determined the linear sequence of genes to be aroB-ompB-malQP-glpD.