LOCALIZATION OF ADP-RIBOSYLATION FACTOR DOMAIN PROTEIN-1 (ARD1) IN LYSOSOMES AND GOLGI-APPARATUS

ADP-ribosylation factor domain protein 1 (ARD1) is a member of the ADP ribosylation factor (ARF) family of guanine nucleotide-binding protei ns that differs from other ARFs by the presence of a 46-kDa amino-term inal extension which acts as a GTPase-activating protein (GAP) for its ARF domain. Similar to ARF GAPs, the GAP domain of ARD1 contains a zi nc finger motif and arginine residues that are critical for activity. It differs from other ARF GAPs in its covalent association with the GT P-binding domain and its specificity for the ARF domain of ARD1. ARFs are presumed to play a key role in the formation of intracellular tran sport vesicles and in their movement from one compartment to another. We report here that ARD1 overexpressed in cells, as a fusion or nonfus ion protein, is localized in vesicular structures that are concentrate d mainly in the perinuclear region, but are found also throughout the cytosol, Microscopic colocalization and subcellular fractionation stud ies showed that ARD1 was associated with the Golgi complex and lysosom al structures. ARD1 expressed as a green fluorescent fusion protein wa s initially associated with the Golgi network and subsequently localiz ed to lysosomes, Lysosomal and Golgi membranes isolated from human liv er by immunoaffinity contained native ARD1, Localization to these orga nelles, therefore, did not appear to be a result of overexpression. Th ese observations suggest that the ARF-related protein ARD1 may play a role in the formation or function of lysosomes and in protein traffick ing between Golgi and lysosomes.