Uvomorulin-catenin complex formation is regulated by a specific domain in the cytoplasmic region of the cell adhesion molecule.

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Abstract
We have recently found that the cytoplasmic region of the cell adhesion molecule uvomorulin associates with three proteins named catenin alpha, beta, and gamma. Here we show by analysis of various mutant uvomorulin polypeptides expressed in mouse L cells that this association is mediated by a specific domain in the cytoplasmic region. A specific recognition site for catenins is located in a 72-amino acid domain. Interestingly, 69 of the 72 amino acid residues are encoded by a single exon of the uvomorulin gene. To demonstrate the direct interaction between catenins and the 72-amino acid domain, cDNA constructs composed of H-2Kd cDNA and various 3' sequences of uvomorulin were expressed in L cells. Chimeric proteins between H-2Kd and the 72-amino acid domain of uvomorulin were shown, by immunoprecipitation with anti-H-2Kd antibodies, to complex with catenin alpha, beta, and gamma. Catenins connect uvomorulin to cytoskeletal structures. We provide biochemical evidence for an association of the uvomorulin-catenin complex with actin bundles. Our results suggest that catenin alpha plays a key role in the association with actin filaments, whereas catenin beta binds more directly to the cytoplasmic region of uvomorulin. In cell aggregation assays with transfected cells expressing normal or mutant uvomorulin, the adhesive function was expressed only when uvomorulin was associated with catenins. From these results we conclude that the cytoplasmic anchorage of uvomorulin is of major biological importance.