A novel RING finger in the C-terminal domain of the coatomer protein α-COP

The C-terminal domain of alpha-COP, an essential subunit of the COPI coatomer complex, is composed of an all alpha- helical region and a small beta-sheet domain. We show that this beta-sheet domain is a Really Interesting New Gene (RING)-like treble clef zinc finger. The zinc-binding residues are substituted by other aminoacids in many homologs including the structurally-characterized proteins from Saccharomyces cerevisiae and Bos taurus. This RING-like domain is possibly related to those of other vesicle membrane-associated complexes, such as CORVET, HOPS and SEA, and likely mediates interactions with Dsl1p and assist in coat oligomerization.