Reusch, UweUweReuschBernhard, OlafOlafBernhardKoszinowski, UlrichUlrichKoszinowskiSchu, PeterPeterSchu2018-11-072018-11-072002https://resolver.sub.uni-goettingen.de/purl?gro-2/38189Heterotetrameric adaptor-protein complexes AP-1A and AP-3A mediate protein sorting in post-Golgi vesicular transport. AP-1A and AP-3A have been localized to the trans -Golgi network, indicating a function in protein sorting at this compartment. AP-3A appears to mediate trans -Golgi network-to-lysosome and also endosome-to-lysosome protein sorting. AP-1A is thought to be required for both trans -Golgi network-to-endosome transport and endosome-to-trans -Golgi network transport. However, the recent discovery of a role for monomeric GGA (Golgi localized gamma-ear containing, ARF binding protein) adaptor proteins in trans -Golgi network to endosome protein transport has brought into question the long-discussed trans -Golgi network-to-endosome sorting function of AP-1A. Murine cytomegalovirus gp48 contains an unusual di-leucine-based lysosome sorting signal motif and mediates lysosomal sorting of gp48/major histocompatibility complex class I receptor complexes, preventing exposure of major histocompatibility complex class I at the plasma membrane. We analyzed lysosomal sorting of gp48/major histocompatibility complex class I receptor complexes in cell lines deficient for AP-1A, AP-3A and both, to determine their sorting functions. We find that AP1-A and AP3-A mediate distinct and sequential steps in the lysosomal sorting. Both sorting functions are required to prevent MHC class I exposure at the plasma membrane at steady-state.enjournal_article10.1034/j.1600-0854.2002.31007.x12230473000178003100007