GMAP-210, a cis-Golgi network-associated protein, is a minus end microtubule-binding protein

We report that a peripheral Golgi protein with a molecular mass of 210 kD l ocalized at the cis-Golgi network (Rios, R.M., A.M. Tassin, C, Celati, C, A ntony. M.C. Boissier. J.C, Homberg, and M. Bornens, 1994. J. Cell Biol. 125 :997-1013) is a microtubule-binding protein that associates in situ with a subpopulation of stable microtubules. Interaction of this protein, now call ed GMAP-210, for Golgi microtubule-associated protein 210, with microtubule s in vitro is direct, tight and nucleotide-independent. Biochemical analysi s further suggests that GMAP-210 specifically binds to microtubule ends. Th e full-length cDNA encoding GMAP-210 predicts a protein of 1,979 amino acid s with a very long central coiled-coil domain. Deletion analy ses in vitro show that the COOH terminus of GMAP-210 binds to microtubules whereas the N H2 terminus binds to Golgi membranes. Overexpression of GMAP-210-encoding c DNA induced a dramatic enlargement of the Golgi apparatus and perturbations in the microtubule network. These effects did not occur when a mutant lack ing the COOH-terminal domain was expressed. When transfected in fusion with the green fluorescent protein, the NH2-terminal domain associated with the cis-Golgi network whereas the COOH-terminal microtubule-binding domain loc alized at the centrosome. Altogether these data support the view that GMAP- 210 serves to link the cis-Golgi network to the minus ends of centrosome-nu cleated microtubules, In addition, this interaction appears essential for e nsuring the: proper morphology and size of the Golgi apparatus.