SDS-PAGE comparison of proteins in recombinant strains of E. coli TOP10F′ containing xynTB coding regions in the forward (pLOI3708) and reverse (pLOI3707) orientations with respect to the lac promoter. Cells were grown and harvested as described for xylosidase assays. Lanes: M, protein standards with molecular mass in kilodaltons indicated on the left; 1, TOP10F′(pLOI3708) without IPTG; 2, TOP10F′(pLOI3708) with 1 mM IPTG; 3, TOP10F′(pLOI3707) without IPTG; 4, TOP10F′(pLOI3707) with 1 mM IPTG. The arrow denotes a 65-kDa band in lane 2 corresponding to XynB.