The invention belongs to the field of thrombolysis and of tissue plasminogen activator (tPA) derivative production in prokaryotic cells. The invention relates to methods for the production of a recombinant DNA-derived tPA, a variant thereof or a (Kringle 2 Serine) K2S molecule or a variant thereof in prokaryotic cells, wherein the tPA or K2S or variant is secreted extracellularly as an active and correctly folded protein, and the prokaryotic cell contains and expresses a vector comprising the DNA coding for the tPA or K2S or variant operably linked to the DNA coding for the signal peptide OmpA. The invention further relates to specific K2S derivatives obtainable by the method. The invention further relates to the DNA molecules and the use of the DNA molecules in the methods.