Formation of complexes involving SNARE proteins present on apposed membranes plays an important role in membrane fusion – for example,duringCa2+-triggered exocytosis of secretory vesicles. It is often assumedthat SNAREs directly drive the fusion process, but is this really the case?Joshua Zimmerberg and co-workers now show that it is not (see p. 2087). They have used proteases to selectively remove specificSNAREs from sea urchin vesicles,quantified the remaining SNAREs precisely by high-sensitivity immunoblotting and monitored the performance of the vesicles in fusion assays. Surprisingly,the authors find that removing SNAREsdoes not stop vesicles fusing. Further proteolysis of vesicles from which the SNARES have been removed does abolish fusion, however, which suggests that proteins other than SNAREs drive the fusion process. Zimmerberg and co-workers therefore propose that SNAREs function in events prior to fusion –for example, in vesicle docking or priming. Interestingly, their studies with the protease papain reveal that SNARE...

You do not currently have access to this content.