A SNARE required for retrograde transport to the endoplasmic reticulum

SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) are central components of the machinery mediating membrane fusion in all eukaryotic cells. Sequence analysis of the yeast genome revealed a previously uncharacterized SNARE, SNARE-like tail-anchored protein 1 (SIt1). SIt1 is an essential protein localized in the endoplasmic reticulum (ER). It forms a SNARE complex with Sec22 and the ER syntaxin Well. Down-regulation of SIt1 levels leads to improper secretion of proteins normally resident in the ER. We suggest that SIt1 is a component of the SNAREpin required for retrograde traffic to the ER. Based on the previously reported association with Ufe1 and Sec22, Sec20 likely contributes the fourth SNARE to the SNAREpin.