The SXYQRL sequence in the cytoplasmic domain of TGN38 plays a major role in trans-Golgi network localization

The trans-Golgi network (TGN) plays a central role in protein sorting/targeting. TGN38 is an integral membrane protein confined mainly to the TGN. When the cytoplasmic 32-residue sequence of TGN38 was fused to the ecto- and transmembrane domains of glycophorin A (a surface protein), the resulting chimeric protein was localized to the TGN. Detailed mutagenesis of the 32-residue sequence revealed that the Ser, Tyr, and Leu residues at positions 23, 25, and 28, respectively, are essential for TGN localization. Further studies demonstrate that the sequence SXYQRL can by itself confer significant TGN localization.