Current Project(s) :

Biogenesis and maintenance of endoplasmic reticulum exit sites.

To meet the needs of secreted and membrane proteins, RNA is translated at the ER and the nascent polypeptide chains are inserted into its lumen. After proper folding and initial posttranslational modification, the proteins are transported to the Golgi for further posttranslational modifications. The mature proteins are eventually delivered to their final destinations in- and outside the cell.

The anterograde transport step from ER to Golgi is accomplished by coated vesicles and tubules, which form at the donor membrane. The forces needed to deform the membrane into buds and to finally pinch off cargo-laden vesicles are exerted by proteins assembling to a so-called COPII coat. The pinching off of vesicles, the (de)stabilisation and the (dis)assembly of the coat are not yet fully elucidated and so far even less is known about the regions on the ER membrane, where these coat components assemble and vesicles bud – the so-called ER exit sites (ERES).

ERES are distinct COPII-enriched regions on the ribosome-free ER where protein export takes place. Their diameter is approximately 0.5 – 1 μm and a eukaryotic cell contains several hundreds of these sites with the actual number being dependent on the stage of the cell cycle. ERES as quite long-lived structures which are not very mobile can fuse, undergo fission and be de novo synthesised. Up to now there are only speculations about what defines the location and the maintenance of these sites.

We made it our objective to contribute to the understanding of ERES organisation and thus aim at identifying and characterising proteins involved in the process of ERES biogenesis and maintenance. In order to find candidate proteins with this so far unanticipated role, a screen of proteins from the EMBL/DKFZ GFP-ORF database [Simpson et al., 2000 and http://gfp-cdna.embl.de] is currently being done. Proteins identified will be further investigated with the goal to describe their subcellular localisation and to find their interaction partners what eventually should allow us to deduce a possible interaction mechanism behind ERES formation.