Editing Functional genomics (section)

====Yeast two-hybrid system====
{{Main|Two-hybrid screening}}
A yeast [[two-hybrid screening]] (Y2H) tests a "bait" protein against many potential interacting proteins ("prey") to identify physical protein–protein interactions. This system is based on a transcription factor, originally GAL4,<ref name=pmid2547163>{{cite journal | vauthors = Fields S, Song O | title = A novel genetic system to detect protein-protein interactions | journal = Nature | volume = 340 | issue = 6230 | pages = 245–6 | date = July 1989 | pmid = 2547163 | doi = 10.1038/340245a0 | bibcode = 1989Natur.340..245F | s2cid = 4320733 }}</ref> whose separate DNA-binding and transcription activation domains are both required in order for the protein to cause transcription of a reporter gene. In a Y2H screen, the "bait" protein is fused to the binding domain of GAL4, and a library of potential "prey" (interacting) proteins is recombinantly expressed in a vector with the activation domain. In vivo interaction of bait and prey proteins in a yeast cell brings the activation and binding domains of GAL4 close enough together to result in expression of a [[reporter gene]]. It is also possible to systematically test a library of bait proteins against a library of prey proteins to identify all possible interactions in a cell.