Use1p is a
yeast SNARE protein required for retrograde traffic from the Golgi to the ER.
Meik Dilcher (1), Subbulakshmi Chidambaram (1), Beate Veith (1), Enno
Hartmann (2), Hans-Dieter Schmitt (3), Gabriele Fischer von Mollard (1)
(1) Biochemistry II, University of Goettingen, Heinrich-Dueker W 12,
Goettingen, 37073, Germany (csubbul@gwdg.de); (2) Institut für Biologie,
Medizinische Universität zu Lübeck, 23538 Lübeck, Germany; (3) Abteilung
Molekulare Genetik, Max-Planck-Institut für biophysikalische Chemie, 37070
Göttingen, Germany
SNAREs have important roles in vesicle targeting and fusion. SNAREs on transport vesicles and target membranes form complexes via SNARE motifs. With the advance of sequencing projects all members of protein families can be identified if sequence homologies are sufficient. As the genome of the yeast Saccharomyces cerevisiae is fully sequenced it was thought that all yeast SNAREs were known. Here we describe a novel yeast protein with a typical SNARE motif but with low overall amino acid homologies to other SNAREs. The protein localized to the ER and was therefore named Use1p (unconventional SNARE in the ER). Antibodies directed against Use1p coimmunoprecipitated the SNAREs Ufe1p, Sec20p and Sec22p, which are required for retrograde traffic from the Golgi to the ER. Use1p bound neither Bos1p nor Bet1p which are SNAREs in anterograde traffic from the ER to the Golgi. A temperature sensitive use1 mutant was generated. use1 mutant cells accumulated the ER form of CPY and invertase. More specific assays revealed that use1 mutant cells were defective in retrograde traffic to the ER. This was supported by strong genetic interactions between USE1 and the genes encoding SNAREs in retrograde traffic to the ER. Therefore, we conclude that Use1p is a novel SNARE protein which functions in retrograde traffic from the Golgi to the ER.