Misdirection leads the way to vesicle transport proteins

Misdirection leads the way to vesicle transpor t proteins Bentley et al. use a novel assay to identify the kinesin motor proteins that bind to different types of endosomes. Membrane traf-fi cking is controlled by a large number of proteins that bind to spe-cifi c vesicles and organelles. But defi ning which proteins bind to which membranes within a crowded cell—by fl uorescence co-localization, for example—is often diffi cult. Bentley et al. therefore developed an assay that can directly test whether a protein binds to a specifi c vesicle population in vivo. The researchers fused candidate proteins to an FRB tag that, in the presence of a rapamycin-like drug called AP21967, binds to an FKBP-tagged version of the dynein motor adaptor molecule Bicaudal D2. If a candidate protein binds to a specifi c vesicle population, dynein will be recruited to these organelles in the presence of AP21967 and subsequently transport them to the minus ends of microtubules, which, in most cell types, are clustered around a microtubule-organizing center (MTOC) in the middle of the cell. Bentley et al. verifi ed their assay by showing that an FRB-tagged version of the small GTPase Rab5 could misdirect early endosomes to microtubule minus ends, whereas FRB-Rab7 caused late endosomes to cluster around the MTOC. The researchers then systematically analyzed the endosome-binding properties of Kinesin-3 family members and found that KIF13A and KIF13B bound to early endosomes, whereas KIF1A and KIF1B␤ associated with late endosomes and lysosomes. Bentley et al. think that the approach should be applicable to many other families of membrane traffi cking proteins as well. Gaik et al. describe the P-shaped structure of a key protein complex at the cyto-plasmic face of nuclear pores. The nuclear pore complex (NPC) consists of ‫03ف‬ different nucleoporins, most of which are organized into stable subcomplexes. The Nup82 subcomplex, comprising the nucleoporins Nup82, Nup159, Nsp1, and the dynein light chain Dyn2, localizes to the cytoplas-mic face of NPCs where it promotes mRNA export. How the subcomplex assembles and fi ts in to the rest of the NPC is unclear, however. Gaik et al. purifi ed the Nup82 complex from yeast and analyzed its structure using several different techniques. Most Nup82 complexes contained 2 copies of each nucleoporin and 10 Dyn2 molecules. Although Nup82, Nup159, and Nsp1 all contain ␣-helical domains predicted to form coiled-coil dimers, electron microscopy showed that the complex didn't adopt an extended, …