THE ROLE OF IG-BETA IN PRECURSOR B-CELL TRANSITION AND ALLELIC EXCLUSION

Lymphocytes express multicomponent receptor complexes that mediate div erse antigen-dependent and antigen-independent responses. Despite the central role of antigen-independent events in B cell development, litt le is known about the mechanisms by which they are initiated. The asso ciation between the membrane immunoglobulin (Ig) M heavy chain (m mu) and the Ig alpha-Ig beta heterodimer is now shown to be essential in i nducing both the transition from progenitor to precursor B cells and s ubsequent allelic exclusion in transgenic mice. The cytoplasmic domain of Ig beta is sufficient to induce these early antigen-independent ev ents by a mechanism that requires conserved tyrosine residues in this protein.