Btn2p is a novel coiled coil cytosolic protein in Saccharomyces cerevisiae. We report that Btn2p interacts with Yif1p, a component of a protein complex at the Golgi that functions in ER to Golgi transport. Deletion of Btn2p, btn2-Delta, results in mis-localiztion of Yif1p to the vacuole. Therefore, Btn2p may have an apparent role in intracellular trafficking of proteins. Btn2p, was originally identified as being up-regulated in a btn1-Delta strain, which exhibits dysregulation of vacuolar pH, and this up-regulation of Btn2p was presumed to contribute to maintaining a stable vacuolar pH [Pearce et al. Nat. Genet. 22 (1999) 55]. We propose that upregulation of Btn2p in btn1-Delta is an indicator of altered trafficking within the cell, and as btn1-Delta serves as a model for the lysosomal storage disorder Batten disease, that altered intracellular trafficking may contribute to some of the cellular pathological hallmarks of this disease. (C) 2003 Elsevier Science (USA). All rights reserved.