Coomassie brilliant blue stained SDS-PAGE showing recombinant TK0522 in the intracellular (lanes 1–3) and extracellular (4–6) fractions. Lane M, molecular weight marker; lane 1 and 4, cells containing pET-21a(+) at 20 h post-induction; lane 2 and 5, cells containing pET-TK0522 at 4 h post-induction; lane 3 and 6, cells containing pET-TK0522 at 20 h post-induction.