Figure 6.

Features of the TR basolateral sorting signal. Residues 19–41, which are necessary and sufficient for basolateral sorting of TR, are shown. Each of the two four-residue sequences within this region that are predicted to adopt a tight turn conformation, the YTRF internalization signal and the sequence GDNS (Collawn et al., 1990), are underlined. The region most important for basolateral sorting is within residues 29–41, and the TR basolateral sorting signal is neither tyrosine based nor colinear with the YTRF internalization signal. Also indicated is the four-residue sequence RQVD, which is similar to the sequence RNVD found to be important for basolateral sorting of pIgR (Aroeti et al., 1993). However, the sequence RQVD is not required for basolateral sorting of TR, and neither Val-29 nor Val-36 is important for activity of the TR basolateral sorting signal.