The distinct peripheral cytosolic proteins, alpha, beta and gamma-catenin (102, 94 and 86 kDa) found in many tissues bind to the conserved cytoplasmic tail domain of the cell-adhesion cadherins. Catenins link E-cadherin to other integral membrane or cytoplasmic proteins and are modulated by Wnt-1 proto-oncogene. They are good candidates for mediating transduction of cell-cell contact positional signals to the cell interior. Absence of alpha-catenin is found in certain tumor cell lines and reduced levels in certain human carcinomas. Beta-catenin binds directly to the cytoplasmic tail of E-cadherin. It binds to the N-terminus of alpha-catenin and interacts with the protein product of the tumor suppressor gene APC. This interaction involves a 15-aa repeat in the APC. Beta-catenin cell levels seem to be controlled by APC. The central core region of beta-catenin is involved in mediation of cadherin-catenin complex interaction with EGFR.