LIM DOMAIN RECOGNITION OF A TYROSINE-CONTAINING TIGHT TURN

Endocytosis of cell surface receptors requires sequence ''codes'' cons isting of tight turn structures with an essential Tyr or Phe residue. To determine mechanisms through which cells recognize this information , we utilized exon 16 of the human insulin receptor in the two-hybrid system to isolate a novel 455-amino acid cytoplasmic protein that cont ains two LIM domains within its carboxyl terminus. Mutational analyses indicate that one of the Cys-rich Zn2+ binding LIM domains specifical ly recognizes active but not inactive endocytic codes contained in exo n 16. These findings suggest that LIM domain structures in proteins pr ovide molecular recognition of Tyr-containing tight turn structures.