Recruitment to Golgi membranes of ADP-ribosylation factor 1 is mediated bythe cytoplasmic domain of p23

Binding to Golgi membranes of ADP ribosylation factor 1 (APF1) is the first event in the initiation of COPI coat assembly. Based on binding studies, a proteinaceous receptor has been proposed to be critical for this process. We now report that p23, a member of the p24 family of Golgi-resident transm embrane proteins, is involved in ARF1 binding to membranes. Using a cross-l ink approach based on a photolabile peptide corresponding to the cytoplasmi c domain of p23, the GDP form of ARF1 (ARF1-GDP) is shown to interact with p23 whereas ARF1-GTP has no detectable affinity to p23. The p23 binding is shown to localize specifically to a 22 amino acid C-terminal fragment of AR F1. While a monomeric form of a non-photolabile p23 peptide does not signif icantly inhibit formation of the cross-link product, the corresponding dime ric form does compete efficiently for this interaction. Consistently, the d imeric p23 peptide strongly inhibits ARF1 binding to native Golgi membranes suggesting that an oligomeric form of p23 acts as a receptor for ARF1 befo re nucleotide exchange takes place.