Fig 10.

One-hybrid systems. (A) DNA-protein interactions (706). A putative DNA-binding protein Y is in fusion with the Gal4 activation domain. Interaction of protein Y with a promoter X stimulates reporter gene expression. This assay can single out proteins that bind a fixed promoter of interest or DNA sequences that are targeted by a fixed DNA-binding protein of interest. (B) Identification of transcriptional activity (696). A chimeric protein with the Gal4 DNA-binding domain and a transcriptional activator (a nuclear receptor [NR] in this example) stimulates expression of a reporter gene under the control of Gal upstream activating sequences. An application of such a system is the identification of ligands that trigger NR nuclear import and activity. AD, activation domain; DBD, DNA-binding domain; Pol, polymerase; UAS, upstream activating sequence.