Analysis of IscU expression and purification. (A) SDS/PAGE of overproduction and purification. Lane 1, molecular weight standards; lane 2, BL-21 cells harboring pTrcIscU (25 μg of protein); lane 3, BL-21 cells harboring pTrcIscU plasmid grown for ≈16 h after IPTG induction (25 μg of protein); lanes 4–6, purified IscU. (B) Immunoblot analysis of constitutive IscU expression in W3110, DH5α, and BL-21 cells grown to stationary phase in Terrific Broth. Lanes 1–3, purified IscU; lanes 4–6, E. coli whole cells (15 μg of protein each).