Abstract: The present invention is directed to methods of screening populations of transgenic cells for cells that produce a protein of interest. The methods comprise culturing transgenic cells in culture conditions that include at least one non-natural amino acid (nnAA) in the cell culture medium. The transgenic cells comprise at least one polynucleotide that codes for a fusion protein with a first domain coding for a protein of interest and a second domain coding for a domain that facilitates detection of the transgenic cells that express the protein of interest when the transgenic cell expresses the second domain.