Production of recombinant proteins utilizing non-antibiotic selection methods and the incorporation of non-natural amino acids therein

Provided herein are methods and compositions for expression of a nucleic acid construct comprising nucleic acids encoding a) a recombinant polypeptide, and b) a prototrophy-restoring enzyme in a host cell that is auxotrophic for at least one metabolite. In various embodiments, the host cell is auxotrophic for a nitrogenous base compound or an amino acid. The invention involves introducing an analogue into the growth media for the host cell such that the analogue is incorporated into the recombinant polypeptide or a nucleic acid coding sequence thereof. In various embodiments, the compositions and methods disclosed herein result in improved recombinant protein expression compared to expression of recombinant protein in an antibiotic selection system, or compared to expression of the recombinant protein in an expression system that lacks a metabolite analogue.