Title: Molecular Interaction between Limb Deformity Proteins (Formins) and Src Family Kinases
Abstract: Ld proteins (formins) are encoded by the <i>limb deformity</i> (<i>ld</i>) gene and define a family of related gene products regulating establishment of embryonic polarity. In this study we establish that chicken and murine Ld proteins interact directly with Src family kinases (c-Src and c-Fyn). Specific binding is mediated by the proline-rich domain present in Ld proteins and the ligand binding surface of the Src SH3 domain. Co-immunoprecipitation of Ld and c-Src proteins from transfected cells shows that these proteins associate <i>in vivo</i>. Immunolocalization and biochemical fractionation of fibroblasts confirms the predominant nuclear localization of Ld proteins, but unexpectedly identifies a population of Ld proteins associated to cellular membranes. This population of Ld proteins co-localizes with membrane-associated c-Src proteins at both plasma and perinuclear membranes. These studies indicate that the morphoregulatory Ld proteins interact with signal transduction cascades by association to membrane-bound Src family kinases.