Transport proteins are crucial to maintaining physiological homeostasis within all organisms. They are used to traffic compound like inflammatory mediators, hormones, and ions, and eliminate compounds such as bile acids, organic anions, and toxicants from cells and ultimately from the organisms. As such, understanding how these proteins function and are regulated, as well as knowing their substrates and potential inhibitors, is crucial to understanding normal physiology, the causes and results of disease states, and drug-drug interactions. We propose to clone and determine the 5'-promoter sequences of the human organic anion transporters (OATs), specifically OAT1, OAT2, OAT3, and OAT4. These proteins function in the secretion of anionic endogenous and exogenous substrates from the blood into the renal proximal tubules for ultimate efflux into the tubule lumen, or during tubular reabsorption. We propose to clone and express these organic anion transporters into LLC-PK1 cells, a polarized kidney epithelial cell line, to determine their substrate specificity. We will also determine their regulation by cloning their 5'-upstream response elements into HepG2 cells to determine transcriptional activation by nuclear orphan receptors. Finally, we will also determine whether any other homologues are present in the kidney by cDNA library screening. We hypothesize that understanding the function and regulation of these transporters will enable us to better predict drug-drug interactions and the regulation of the tubular secretion of endogenous ligands.