A HUMAN HOMOLOG CAN FUNCTIONALLY REPLACE THE YEAST VESICLE-ASSOCIATEDSNARE VTI1P IN 2 VESICLE TRANSPORT PATHWAYS

Membrane traffic in eukaryotic cells requires the interaction of a ves icle-associated soluble NSF attachment protein receptor (v-SNARE) on t ransport vesicles with a SNARE on the target membrane (t-SNARE). Recen tly, we identified the yeast protein Vti1p as a v-SNARE that is involv ed in two transport reactions. Vti1p interacts with the prevacuolar t- SNARE Pep12p in Golgi to prevacuolar transport and with the cis-Golgi t-SNARE Sed5p in traffic to the cis-Golgi. Here we describe a human Vt i1p homolog, hVti1, Whereas vti1 Delta cells are inviable, expression of hVti1 allows vti1 Delta cells to grow at nearly the wild-type growt h rate. When expressed in yeast hVti1 can replace Vti1p in both Golgi to prevacuolar transport and in traffic to the cis-Golgi, Sequence com parisons with a Schizosaccharomyces pombe and two different mouse Vti1 homologs led to the identification of a very conserved predicted alph a-helix. Amino acid exchanges in vti1 mutant alleles defective either in one or both trafficking steps cluster in this domain, suggesting th at this structure is probably the binding site for effector proteins.