The present invention relates to a host organism containing recombinant nucleic acids coding for the vitamin K reductase complex subunit 1 (VKORC1) and recombinant nucleic acids coding for a vitamin K dependent (VKD) protein, wherein both the recombinant VKORC1 and the recombinant VKD protein are expressed in said host organism. Further, the present invention relates to a cell culture system comprising cells which contain said recombinant nucleic acids and to methods for improving the productivity of recombinant VKD protein expression in a host organism being cultured in suitable systems.