Estimation of the expression of different SmQnr alleles in E. coli. M, molecular mass standards, lane 2, E. coli KZM120 (ΔacrAB) carrying pGEM-T (negative control), (A) Expression of SmQnr by E. coli strains containing different plasmids that encode different SmQnr alleles. The SmQnr protein used for its identification by MS-MALDI-TOF (see Methods) was the allele encoded by pBS3.13. (B) To establish the effect of the level of expression of SmQnr on the susceptibility to antibiotics, the original clone (1) and two re-transformants (2 and 3) were analysed for each of the plasmids pBS3.8, pBS3.13 and pBS3.25. The position of SmQnr is indicated with an arrow.