Purification of PulD. Pooled PulD-containing fractions at each step in the purification were analyzed by SDS/PAGE (4–20% acrylamide), and then stained with Coomassie brilliant blue. The 68-kDa band in the PulD-containing peak from the Q Sepharose column is not PulD. The positions of multimeric and monomeric PulD and PulS are indicated. The sizes of the molecular mass markers (extreme right and left lanes) are (from top to bottom) 212, 158, 116, 97, 66, 56, 43, 36, 26, 20, 14, and 7 kDa.