Figure 1.

Residues 19–41 of the TR cytoplasmic tail are necessary and sufficient to target TR to the basolateral surface of MDCK cells. Filter-grown MDCK cells expressing wild-type and mutant TR were incubated either apically or basolaterally for 1 h at 4°C with ¹²⁵I-labeled Tf (4 μg/ml). After washing away unbound Tf, the amount of ¹²⁵I-labeled Tf specifically bound on each surface was determined (mean ± standard error of three independent experiments).