Localization of TGN38 to the trans-Golgi network: involvement of a cytoplasmic tyrosine-containing sequence

Having established that the cytoplasmic tail of TGN38 was sufficient to confer TGN localization on another protein, we attempted to further delineate the sequences and specific amino acid residues that were critical for this function. To this end, COOH-terminal truncated forms of T-T-G were constructed and transiently expressed in NRK cells (Fig. 4 , A1-A3). Removal of the last four amino acids from the COOH-terminus resulted in a protein that was still localized to a TON-like structure (Fig. 4, A1) and colocalized with endogenous TGN38 (not shown). This was in contrast to A2 and constructs with more extensive truncations, all of which showed prominent staining of the plasma membrane (Fig. 4 , A2 and A3). These results implicated the sequence YQRL as containing information necessary for TON localization. A series of internal deletion mutants of A1 (Fig. 4,