The structurally related exbB and tolQ genes are interchangeable in conferring tonB-dependent colicin, bacteriophage, and albomycin sensitivity.

Double exbB tolQ mutants of Escherichia coli were completely resistant to bacteriophages T1 and phi 80, in contrast to strains with exbB or tolQ mutations, which were sensitive. Cells carrying mutations in exbB were partially tolerant to colicins B, D, and M and became fully tolerant by the introduction of tolQ mutations. This suggested involvement of both exbB and tolQ in tonB-dependent uptake.