Practice question

Final readout in yeast two-hybrid is based on transcriptional activation of reporter cassettes integrated downstream of Gal4-responsive promoters. If bait and prey physically associate, the activation domain is tethered to promoter, stimulating transcription of genes enabling growth on selective media lacking histidine or adenine, or colorimetric enzymes like beta-galactosidase. Thus survival, colony color, or luminescence reflects interaction strength. Fluorescence intensity, radiolabel, or sequencing are not primary outputs, although secondary validation may use them. The system converts protein interaction into a genetic readout amenable to selection.