SIGNALING-DEFECTIVE MUTANTS OF THE B-LYMPHOCYTE ANTIGEN RECEPTOR FAILTO ASSOCIATE WITH IG-ALPHA AND IG-BETA GAMMA/

The B cell receptor for antigen, the membrane immunoglobulin (mIg) mol ecule, is normally expressed in association with at least two other pr oteins, mb-1 (Ig-alpha) and B29 (Ig-beta/gamma). We have previously de scribed a set of murine B cell clones transfected with wild-type and m utated forms of membrane-bound IgM (mIgM) that vary in their ability t o transduce signals to the cell interior. Analysis of the B cell recep tor complex in signaling and nonsignaling mutants of mIgM reveals comp lete concordance between intact signaling ability and ability of the m IgM to associate with Ig-alpha and Ig-beta/gamma. These results point to the importance of the mIgM transmembrane region in mediating bindin g to accessory molecules, and provide support for a role of Ig-alpha a nd Ig-beta/gamma that extends beyond surface expression to signal tran sduction in B lymphocytes.