PBP expression over growth. Strain Newman pME2, carrying mecA, and its secDF mutant were cultivated in LB and samples collected at the indicated OD600 were used to prepare membrane fractions. (A) Membranes were incubated with the fluorescent penicillin analogue Bocillin-FL. Bands corresponding to PBPs 1-3 are indicated. (B) Western blot analysis of membrane fractions using antibodies against PBP2a and PBP4, respectively.