Endocytosis of surface proteins through clathrin-coated pits requires an internalization
signal in the cytoplasmic domain. Two types of internalization signal have been described:
one requiring a tyrosine as the critical residue (tyrosine-based motif), and the other
consisting of either two consecutive leucines or an isoleucine and leucine (dileucine motif).
Although it seems that these signals are necessary and sufficient for endocytic targeting, the
mechanism of recognition is not well understood. To examine this question, tetracycline …