FIGURE 1.

A, a schematic representation of the conserved motifs in DrrA. Previously identified motifs, located in the N-terminal domain of DrrA, include Walker A, Q-loop, signature, Walker B, and the switch motif (34). The motifs identified in this study, which include LDEADQLA, LDEVFL, and CREEM, are located in the C-terminal domain of DrrA. Numbers indicate the locations of specific amino acid residues. The position of residue 319 is also marked. B, effect of mutations in the CREEM on expression of DrrA and DrrB. Membranes were prepared as described under “Experimental Procedures.” 15 μg of membrane protein was analyzed on 12% SDS-polyacrylamide gels, followed by Western blot analysis with anti-DrrA (top), anti-DrrB (middle), and anti-SecY (bottom) antibodies. A nonspecific band of about 28 kDa was detected in the anti-DrrB blot in control membranes as well as membranes containing DrrAB proteins. Densitometric scanning of the bands in these blots was carried out as described under “Experimental Procedures.” Anti-SecY blot served as a loading control. C and D, histograms showing DrrA and DrrB expression, respectively, in various CREEM mutants. The wild type expression level was designated as 1. The data presented are averages of three independent experiments. Error bars, S.D.