Fig. 4. Class A PBPs are essential for transforming new peptidoglycan into a CbpD-B6-resistant form. The figure shows a schematic presentation of the sensitivity to CbpD-B6 in different genetic backgrounds based on CbpD-B6-resistance assays (see Fig. 3 and supplementary Fig. S5 for relevant growth curves). Development of the S1, R and S2 phases is indicated with the relevant concentration of oxacillin shown on top. Strain khb321 expressing a low-affinity PBP2x (LA-PBP2x) did not develop the R-phase. The same pattern was seen for WT cells (RH425) treated with moenomycin for 10 minutes (WT + M) before addition of CbpD-B6. When the class A PBP1a was changed to a low-affinity version (LA-PBP1a, strain khb332), the cells did not develop the S2-phase when treated with supra-MIC concentrations of oxacillin. The double
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