A novel Rab6-interacting domain defines a family of Golgi-targeted coiled-coil proteins.
In recent years, a large number of coiled-coil proteins localised to the Golgi apparatus have been identified using antisera from human patients with a variety of autoimmune conditions . Because of their common method of discovery and extensive regions of coiled-coil, they have been classified as a family of proteins, the golgins . This family includes golgin-230/245/256, golgin-97, GM130/golgin-95, golgin-160/MEA-2/GCP170, giantin/macrogolgin and a related group of proteins - possibly splice variants - GCP372 and GCP364. GM130 and giantin have been shown to function in the p115-mediated docking of vesicles with Golgi cisternae . In this process, p115, another coiled-coil protein, is though to bind to giantin on vesicles and to GM130 on cisternae, thus acting as a tether holding the two together  . Apart from giantin and GM130, none of the golgins has yet been assigned a function in the Golgi apparatus. In order to obtain clues as to the functions of the golgins, the targeting to the Golgi apparatus of two members of this family, golgin-230/245/256 and golgin-97, was investigated. Each of these proteins was shown to target to the Golgi apparatus through a carboxy-terminal domain containing a conserved tyrosine residue, which was critical for targeting. The domain preferentially bound to Rab6 on protein blots, and mutations that abolished Golgi targeting resulted in a loss of this interaction. Sequence analysis revealed that a family of coiled-coil proteins from mammals, worms and yeast contain this domain at their carboxyl termini. One of these proteins, yeast Imh1p, has previously been shown to have a tight genetic interaction with Rab6 . On the basis of these data, it is proposed that this family of coiled-coil proteins functions in Rab6-regulated membrane-tethering events.