Methods of cell selection and modifying cell metabolism

: Described herein are compositions and methods for identifying, selecting, or culturing cells comprising a subject nucleic acid sequence of interest. Generally, a nucleic acid comprising a subject nucleic acid and a sequence encoding an enzyme molecule involved in biosynthesis of an amino acid is introduced into a cell. The cell is then grown on media lacking the amino acid, such that cells comprising the introduced nucleic acid are capable of growth. In some instances, the cell further comprises an inhibitor of the

enzyme molecule to increase the stringency of the selection.