Abstract: Methods are disclosed for producing recombinant thrombin from precursor molecules that do not require activation by Factor Xa. The protein is produced from host cells transformed or transfected with DNA construct(s) containing information necessary to direct the expression of thrombin precursors. Methods for purification of the thrombin precursors are also described. Thrombin precursors produced from transformed or transfected host cells are auto-activated or secreted in an activated form.

Abstract: The present invention provides an expression system for producing a target protein in a host cell comprising a homologously integrated gene encoding T7 RNA polymerase, and a nonintegrated gene encoding a target protein.