Multiadaptor 4.1 and RanBP9 protein family members as putative interaction partners for VARP, a Rab21 GTPase guanine nucleotide exchange factor

VARP is a novel VPS9 domain-containing protein which acts as a guanine nucleotide exchange factor for small GTPases Rab21 and Rab5, regulators of early endocytosis. However, the molecular mechanisms underlying VARP activity regulation and intracellular localization remain unknown. Using protein interaction cloning in yeast we isolated multiadaptor proteins of 4.1 protein family and RanBP9 as putative VARP interaction partners. The interactions revealed might be important for proper intracellular localization of VARP and its functions in early endocytosis.