A YEAST ATP-BINDING CASSETTE-TYPE PROTEIN MEDIATING ATP-DEPENDENT BILE-ACID TRANSPORT

ATP-dependent transport of bile acids is a key determinant of bile flo w in mammalian liver and is associated with cholesterol excretion, gal lstone formation, and numerous inherited and acquired hepatobiliary di seases, Secretory vesicles and a vacuole enriched fraction purified fr om Saccharomyces cerevisiae also exhibit ATP-dependent bile acid trans port. ATP-dependent transport of bile acids by the vacuolar fraction w as independent of the vacuolar proton ATPase, responded to changes in the osmotically sensitive intravesicular space, and was saturable, exh ibiting a K-m of 63 mu M for taurocholate, The BAT1 (bile acid transpo rter) gene was isolated from yeast DNA by polymerase chain reaction am plification using degenerate oligonucleotides hybridizing to conserved regions of ABC-type proteins, ATP-dependent bile acid transport was a bolished when the BAT1 coding region was deleted from the genome and r estored upon reintroduction of the gene. The deduced amino acid sequen ce predicts that Bat1p is an ABC-type protein 1661 amino acids in leng th, similar to mammalian cMOAT/cMRP1 and MRP1 transporters, yeast Ycf1 p, and two yeast proteins of unknown function. Information obtained fr om the yeast BAT1 gene may aid identification of the gene encoding the mammalian bile acid transporter.