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

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Abstract
To detect specific partners of the small Golgi‐localized GTPase rab1b we generated rab1b mutants and used them as bait proteins in yeast two‐hybrid screens. We isolated several specifically interacting clones. Two of them encode large protein fragments highly homologous to rat GM130 and to human Golgin95. 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.