Fig 1. Purification and visualization of E1-reporter monobodies.

(A) Expression of E1 monobodies conjugated to Rluc8 (left) and EGFP (right) in E. coli. The proteins were purified by HisTrap affinity chromatography. The purified proteins (arrows) were separated by SDS-PAGE and stained with Coomassie blue. M, protein marker; C, non-transformed bacterial lysates; 1, whole lysates from transformed bacteria (one OD₆₀₀ equivalent); 2, supernatants from transformed bacteria; 3, purified proteins (100–200 μg). (B) Light signals from E1-Rluc8 and E1-EGFP. Purified E1-Rluc8 and PBS were mixed with coelenterazine for 1 min, and luminescence was imaged with the NightOWL in vivo imaging system (left). The fluorescence from E1-EGFP was directly imaged with the same system (right).