Purification of MrsD and MrsD H75N. Purification of MrsD (upper part of the figure) and MrsD H75N (lower part of the figure) was followed by SDS-PAGE (A) and immunoblotting (B). Lanes: L and H, low- and high-molecular-mass markers (sizes are in kilodaltons in the left and right margins); 1 and 2, whole-cell lysate of E. coli M15(pREP4)(pQE12 mrsD or pQE12 mrsD H75N) before and after induction with IPTG; 3, cleared cell lysate; 4, HiTrap Q-enriched proteins; 5, MrsD or MrsD H75N purified by gel filtration by using a Superdex 200 PC 3.2/30 column.