Department of Molecular Genetics, Max Planck Institute for Biophysical Chemistry, 37070, Gottingen, Germany-
Abstract: Ypt-Rab GTPases and Sec1-Munc18 -SM- proteins are key components of the membrane fusion machinery- Here, we describe new mutants of the yeast SM protein Sly1 that specifically bypass the need for GTPases Ypt1 and Ypt6 in vesicular transport- All sequence alterations are confined to a short alpha-helix -alpha-20-, which is conserved in fungal Sly1 proteins and, when deleted, results in GTPase suppression- Whereas Sly1p of the evolutionarily distant fission yeast Schizosaccharomyces pombe can functionally replace Sly1p in Sacchromyces cerevisiae, mammalian homologues cannot- This indicates that alpha-20 in fungal Sly1p plays an important role in mediating Ypt-Rab-regulated Sly1p function in membrane fusion-