FIG. 3.

ApbE requires a signal peptide for membrane association and function in thiamine synthesis. (A) The growth of strain DM271 (apbE) carrying pApbE12, encoding wild-type ApbE (●), or pApbE10, encoding ApbE without the lipoprotein signal peptide (■), is shown. Cells were grown in minimal medium with glucose as the sole carbon and energy source and supplemented with 100 nM thiamine where indicated. (B) Immunoblot showing the cellular location of ApbE produced by pApbE10 and pApbE12. Cellular fractions were isolated as described in Materials and Methods. Abbreviations: WC, whole-cell fraction; SOL, soluble cytoplasmic and periplasmic proteins; TM, total membrane proteins.