| Association of Lbc Rho guanine nucleotide exchange factor with alpha catenin related protein , alpha catulin / CTNNAL1 , supports serum response factor activation . ^^^ The Lbc interacting protein has homology with the alpha catenin cell adhesion component and is identical to the alpha catenin like alpha catulin protein of unknown function . ^^^ Here we identify the predicted endogenous alpha catulin product , document alpha catulin and Lbc co expression in multiple human cell lines , and show alpha catulin and Lbc subcellular co fractionation and intracellular localization . ^^^ The required regions for Lbc and alpha catulin interaction were mapped , and complex formation between Lbc and alpha catulin in mammalian cells was detected . ^^^ Functionally , alpha catulin co expression leads to increased Lbc induced serum response factor activation in vivo as measured by a transcriptional reporter assay . ^^^ |