Dsl1p, an Essential Component of the Golgi-Endoplasmic Reticulum Retrieval System in Yeast, Uses the Same Sequence Motif to Interact with Different Subunits of the COPI Vesicle Coat

Dsl1p is required for Golgi-endoplasmic reticulum (ER) retrograde transport in yeast. It interacts with the ER resident protein Tip20p and with δ-COP, a subunit of coatomer, the coat complex of COPI vesicles. To test the significance of these interactions, we mapped the different binding sites and created mutant versions of Dsl1p and δ-COP, which are unable to bind directly to each other. Three domains were identified in Dsl1p: a Tip20p binding region within the N-terminal 200 residues, a highly acidic region in the center of Dsl1p containing crucial tryptophan residues that is required for binding to δ-COP and essential for viability, and an evolutionarily well conserved domain at the C terminus. Most importantly, Dsl1p uses the same central acidic domain to interact not only with δ-COP but also with α-COP. Strong interaction with α-COP requires the presence of comparable amounts of ϵ-COP or β′ -COP. Thus, the binding characteristics of Dsl1p resemble those of many accessory factors of the clathrin coat. They interact with different layers of the vesicle coat by using tandemly arranged sequence motifs, some of which have dual specificity.