Crn7 interacts with AP-1 and is required for the maintenance of Golgi morphology and protein export from the Golgi

Crn7 is a novel cytosolic mammalian WD-repeat protein of unknown function that associates with Golgi membranes. Here, we demonstrate that Crn7 knockdown by small interfering RNA results in dramatic changes in the Golgi morphology and function. First, the Golgi ribbon is disorganized in Crn7 KD cells. Second, the Golgi export of several marker proteins including VSV envelope G glycoprotein is greatly reduced but not the retrograde protein import into the Golgi complex. We further establish that Crn7 co-precipitates with clathrin adaptor AP-1 but is not required for AP-1 targeting to Golgi membranes. We identify tyrosine 288-based motif as part of a canonical YXXPhi sorting signal and a major mu1-adaptin binding site in vitro. This study provides the first insight into the function of mammalian Crn7 protein in the Golgi complex.