Expression analysis and optimization of the expression for the His-tagged US11 protein. (A) Analysis of expressed His-tagged US11 protein and optimization of the IPTG concentration and induction temperature. Lane 1, total protein from BL21 (DE3) with pET32a-US11 before induction; Lanes 2-5, total protein from pET32a-US11 transformed BL21 (DE3) after induction with the concentrations of IPTG: 0.5, 1, 1.5 and 2 mM, respectively. Lanes 6 and 7, total protein from pET-32a-US11 transformed BL21 (DE3) after induction at 30°C and 37°C, respectively. Lane 8, soluble fractions; Lane 9, insoluble fractions; Lane 10, the purified US11 protein after dialysis; Lane M, the protein maker. (B) Optimization of the induction duration. Lanes 1-7, total protein from pET32a-US11 transformed BL21 (DE3) after induction with IPTG (1 mM) for 0, 1, 2, 3, 4, 5 and 6 h, respectively, at 37°C. Lane M, the protein maker. Arrowheads indicate the position of the His-tagged US11 protein.