Identification of two new μ-adaptin-related proteins, μ-ARP1 and μ-ARP2

We report the cDNA cloning, primary structure and tissue distribution of two new proteins homologous to μ-adaptins, the medium chains of the clathrin coat adaptor complexes. Both predicted proteins share 60% amino acid sequence identity with each other and 27–31% identity with μ1-adaptin (ap47) and μ2-adaptin (ap50). Lower similarity (23–25% identity) is found with two other μ-adaptin-related proteins, p47A/B, and there is similarity over the N-terminal 150 amino acids with the adaptin small chains and δ-COP. The mRNAs of both molecules are expressed in all tissues analyzed, but with different profiles of relative abundance. μ-ARP1 is most abundant in brain, ovary and lung, whereas μ-ARP2 is prominently expressed in testis. These proteins suggest the existence of as yet uncharacterized types of clathrin- or non-clathrin-associated protein coats in cellular membrane traffic, of which they are probably prototype subunits, and provide molecular markers and probes for their characterization.