Abstract: The ATP binding cassette (ABC) transporters are important in human health and disease and represent the largest family of transmembrane proteins; however, their highly hydrophobic nature complicates the use of standard biochemical approaches to identify interacting proteins. Here, we report the development of a modified version of the split-ubiquitin membrane yeast two-hybrid (MYTH) technology using genomically integrated "bait" constructs, hence the designation iMYTH. We used iMYTH in a library-screening format and identified six potential interacting partners of the yeast ABC transporter Ycf1p. Strains deleted for several of these genes result in arsenite sensitivity similar to a Deltaycf1 strain. Transport assays show that one of these, Tus1p, a guanine nucleotide exchange factor (GEF) for the small GTPase Rho1p, is a Rho1p-dependent-positive regulator of Ycf1p. Our study provides proof of principle that iMYTH is an ideal methodology to identify physiological interactors and regulators of ABC transporters and other yeast transmembrane proteins.