The present invention relates to nucleic acid molecules comprising a nucleic acid sequence coding for the α- and the β-chain of the human follicle stimulating hormone (FSH), respectively, which has been modified with respect to the codon usage in CHO cells. The present invention further relates to a recombinant nucleic acid molecule comprising such nucleic acid sequences and host cells containing such recombinant nucleic acid molecules, as well as their use in the production of recombinant human FSH. Finally, the present invention also relates to a method for producing host cells expressing human follicle stimulating hormone by transfecting cells in suspension culture under serum-free conditions with the recombinant nucleic acid molecule of the present invention.
