This invention relates to nucleic acid molecules comprising at least one nucleic acid sequence encoding for a peptide or protein of interest, at least one nucleic acid sequence encoding for a selectable marker, and at least one IRES sequence, wherein the at least one IRES sequence is located between the at least one nucleic acid sequence encoding for the peptide or protein of interest and the at least one nucleic acid sequence encoding for the selectable marker. Furthermore, this invention relates to host cells comprising such nucleic acid molecule and to methods of recombinant protein expression using such host cells.