transcription activation domain(ad)was fused to the dna binding(db domain of an E coli protein called LexA; Lexa is a repressor that binds to a known DNA sequence, the LexA operator(LexA OP). Also, the Gal4 DB domain was fused to the ad transcription activation domain of a viral protein know to be a strong activator, VP16. These chimeric proteins were ntroduced into yeast cells with the appropriate Lacz reporter gene constructs and the results of these domain swapping experiments were dramatic. Pe LexA DNA-binding Gal4 activation domain Lacz E Gal4 DNA-bindine VP16 activation domain LexA OP TATA Two Lacz reporter constructs Two chimeric proteins Two derivatives of a Gal4" yeast strain were created one containing the Lacz reporter construct downstream of the GallUAS, and the other containing the Lacz reporter construct downstream of the LexA oP. The two different chimeric proteins were expressed in each strain and the ability to induce lacz activity monitored In addition the following constructs were also introduced into the two strains the Gall UAS LexA OP wild type Gal4 protein 9 al/+aa and a third chimeric 9 al/+oa protein with the Gal4+ activation domain of the Gal4 mutant protein LexA-Gal4AD 十 fused to the lexa db domain the results LexA-Gal4AD from these experiments clearly show that the AD Gal4-VP16AD and the db domains function independently of one another This series of experiments, while interesting and certainly revealing about the how the gal genes are regulated have turned out to have a profound effect on all of biological research because it contributed to the development of a widely used technology called the yeast two hybrid assay. This assay makes possible to determine whether two proteins interact with each other as a complex with long-lived interaction, and sometimes even when two proteins only interact transiently. To determine whether protein X interacts with either protein Y or protein Z one can do the following: fuse protein x to the Gal4 DB this chimeric protein is known as the bait, and it will attach to the UASgal that lies upstream of atranscription activation domain (AD) was fused to the DNA binding (DB) domain of an E. coli protein called LexA; LexA is a repressor that binds to a known DNA sequence, the LexA operator (LexA OP). Also, the Gal4 DB domain was fused to the AD transcription activation domain of a viral protein know to be a strong activator, VP16. These chimeric proteins were introduced into yeast cells with the appropriate LacZ reporter gene constructs and the results of these domain swapping experiments were dramatic. Two LacZ reporter constru er constructs Two chimeric proteins Two derivatives of a Gal4- yeast strain were created, one containing the LacZ reporter construct downstream of the Gal1UAS, and the other containing the LacZ reporter construct downstream of the LexA OP. The two different chimeric proteins were expressed in each strain and the ability to induce LacZ activity monitored. In addition the following constructs were also introduced into the two strains: the wild type Gal4 protein and a third chimeric protein with the activation domain of the Gal481 mutant protein fused to the LexA DB domain. The results from these experiments clearly show that the AD and the DB domains function independently of one another. This series of experiments, while interesting and certainly revealing about the how the Gal genes are regulated, have turned out to have a profound effect on all of biological research because it contributed to the development of a widely used technology called the yeast two hybrid assay. This assay makes it possible to determine whether two proteins interact with each other as a complex with long-lived interaction, and sometimes even when two proteins only interact transiently. To determine whether protein X interacts with either protein Y or protein Z one can do the following: fuse protein X to the Gal4 DB, this chimeric protein is known as the bait, and it will attach to the UASGAL that lies upstream of a