The medium chains of the mammalian clathrin-associated proteins have a homolog in yeast.

We have cloned and sequenced mouse brain AP47, the medium chain of the trans-Golgi network clathrin-associated protein complex AP-1. The predicted protein sequence of AP47 is closely related to rat and calf brain AP50, the corresponding medium chain of the plasma-membrane clathrin-associated protein complex AP-2. We have also identified in the yeast genome an open reading frame encoding a protein of previously unknown function. Referred to here as YAP54, its predicted protein sequence displays a striking homology to AP47. We therefore propose that Yap54 is the medium chain subunit of a putative AP-1 complex in yeast. From the analyses of the optimized sequence alignments of AP47, AP50 and Yap54p, we suggest a model for the domain organization of the medium chains.