Golgins are coiled-coil proteins that are associated with the Golgi apparatus and contribute to its organisation and function (for full review and references see ). Some, such as CASP and golgin-84, have a C-terminal transmembrane anchor, whereas others are peripheral proteins. There is evidence that some of them are tethers that help vesicles to dock with Golgi membranes, a good example being the yeast Uso1 protein and its mammalian homologue p115, which are implicated in ER-Golgi traffic [2, 3]. Yeast Imh1 also plays a role in vesicle traffic to the Golgi . Others have been suggested to link Golgi cisternae, stabilising their stacked morphology, or to act as scaffolds that hold Golgi-associated proteins with regulatory functions . The golgins Bicaudal-D1 and -D2 are thought to link vesicles to the cytoskeleton . Other functions have also been suggested – for example, some golgins might serve to protect membranes from inappropriate fusion events.
Several peripheral golgins have been shown to be anchored to Golgi membranes by association with Rab GTP-binding proteins, the binding site on the golgin often being part of the coiled-coil region. Thus for example Uso1/p115 binds to Ypt1/Rab1 [2, 3], golgin-45 binds Rab2 , and Bicaudal-D binds Rab6 . Other golgins such as Imh1, golgin-97 and golgin-240 share a small GRIP domain at their extreme C terminus, which binds to the GTPase Arl1 and serves to anchor them on Golgi membranes [1, 7].
Coiled-coils often have a structural or spacer function, and as such are not necessarily well-conserved in evolution. Furthermore, their common amphipathic nature means that homology searches can be confusing, all long stretches of coiled-coil showing a superficial similarity. Thus, while some yeast and mammalian golgins share clear structural and functional homology, others are less obviously related.
Our previous studies on the yeast Rab6-like GTPase Ypt6 led to the identification of a protein, Sgm1, that can bind the GTP form of Ypt6 and has the characteristic extensive coiled-coil motifs of a golgin . Moreover, Sgm1 is recruited to Golgi membranes in vivo by Ypt6 . To identify a mammalian homologue, we have localised the Ypt6 binding site and looked for proteins with homology to this region of the protein. This approach identified TMF1/ARA160, which we show to be both localised to the Golgi and capable of binding to all three known isoforms of Rab6. Reduction of the levels of TMF protein by RNAi treatment of NRK cells resulted in an apparent loosening of the overall Golgi structure, with Golgi stacks being spread over a larger area than normal, consistent with a role for the protein in movement, anchoring or tethering of Golgi membranes. TMF1/ARA160 was previously identified by various interaction screens as a DNA-binding protein , a hormone receptor co-activator  and a component of a chromatin remodelling complex . However, our results provide clear evidence that it behaves as a typical golgin.