The present invention relates to modified cDNA sequences coding for factor X polypeptides, in particular human factor X and its derivatives which can bypass the need for either factor VIIIa/FIXa or factor VIIa/TF for activation. The invention relates further to recombinant expression vectors containing such modified cDNA sequences, host cells transformed with such recombinant expression vectors, recombinant polypeptides and derivatives which do have biological activities of the unmodified wild type protein but having altered activation properties, and processes for the manufacture of such recombinant proteins and their derivatives. The invention also covers a transfer vector for use in human gene therapy, which comprises such modified DNA sequences.