The Golgi matrix protein GM130: a specific interacting partner of the small GTPase rab1b

To detect specific partners of the small Golgi-localized GTPase rab1b we ge nerated rab1b mutants and used them as bait proteins in yeast two-hybrid sc reens. We isolated several specifically interacting crones. Two of them enc ode large protein fragments highly homologous to rat GM130 and to human Gol gin95. The full-length human GM130 cDNA was cloned and its interaction with rab1b was characterized in detail by yeast two-hybrid and in vitro binding assays. Here we report for the first time that the rab1b protein interacts specificially with GM130 in a GTP-dependent manner and therefore needs the hypervariable regions of the N- and C-termini. We mapped the rab1b binding site of GM130 and provide evidence that it is different to the previously described p115 and Grasp65 binding sites of the GM130 protein.