Overexpression and purification of FliD. FliD was overexpressed in E. coli host BL21 with the expression vector pET15B (Novagen, Inc.). Lanes: 1, BL21(pET15B) vector control induced with 2 mM IPTG for 4 h at 37°C; 2, BL21(pET15BD) vector with FliD insert uninduced; 3, BL21(pET15BD) vector with FliD insert induced with 2 mM IPTG for 4 h at 37°C; 4, Pharmacia low-molecular-mass (kilodaltons) markers; 5, approximately 400 ng of purified His-FliD protein; 6, approximately 400 ng of purified His-FlaG protein.