Functional membrane association and DNA-binding assays with PutA1294. A, Full-length PutA (100 μg, solid line) and PutA1294 (100 μg, dashed line) were incubated with 60 mM proline, 4 mM o-aminobenzaldehyde, and inverted membrane vesicles from E. coli strain JT31 putA- (0.1 mg/mL membrane protein) in 20 mM Mops buffer (pH 7.5) at 23 °C. The reactions were monitored at 443 nm as previously described (Becker and Thomas, 2001). The calculated specific activities for full-length PutA and PutA1294 are 81 and 8.0 mU mg−1 of membrane protein, respectively. B, Binding mixtures of TRdyed-700 labeled put control DNA (2 nM) and PutA1294 (0, 5, 10, 20, 50, 100, 200, 400, and 800 nM) were incubated at 20 °C for 20 min in 50 mM Tris buffer (pH 7.5, 50 mM NaCl). The PutA1294-DNA complexes were then separated by native polyacrylamide gel (4 %) electrophoresis at 4 °C as previously described (Gu et al., 2004).