Objective To construct a prokaryotic expression vector of Erythrina trypsin inhibitor Variant(rserETI) and use the expression product to purify recombinant tPA.Methods A gene coding for ETI with a subsitution of N-terminal aminal acid Val to Ser(rserETI) was designed.Twelve DNA primers based on the coding sequence for rserETI were synthesized.Full length DNA coding for rserETI was amplified by PCR,digested with restriction endonuclease and cloned into plasmid pET9a.The constructed recombinant plasmid pET9a/...