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Protein-fragment complementation assay
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<p>Within the field of <a href="/facts/Molecular_biology/YgqU35ub">molecular biology</a>, a protein-fragment complementation assay, or PCA, is a method for the identification and quantification of <a href="/facts/Protein%25E2%2580%2593protein_interactions/etvm9Wmg">protein–protein interactions</a>. In the PCA, the proteins of interest ("bait" and "prey") are each covalently linked to fragments of a third protein (e.g. DHFR, which acts as a "reporter"). Interaction between the bait and the prey proteins brings the fragments of the reporter protein in close proximity to allow them to form a functional reporter protein whose activity can be measured. This principle can be applied to many different reporter proteins and is also the basis for the <a href="/facts/Yeast_two-hybrid_system/bBLKUn3T">yeast two-hybrid system</a>, an archetypical PCA assay. </p>