THE IGM ANTIGEN RECEPTOR OF B-LYMPHOCYTES IS ASSOCIATED WITH PROHIBITIN AND A PROHIBITIN-RELATED PROTEIN

The two major classes of antigen receptors on murine B lymphocytes, mI gM and mIgD, are both contained in a complex with two additional molec ules, Ig-alpha and Ig-beta, which permit signal transduction. Accordin gly, early biochemical events after antigen binding to either receptor are similar; biological effects, however, are different. Here, we des cribe three newly discovered intracellular proteins of 32, 37 and 41 k Da molecular mass, that are non-covalently associated with mIgM, but n ot with mIgD. These proteins coprecipitate with mIgM in Triton X-100 a nd Nonidet P-40, but not in digitonin lysates. In addition, mIgM is to some extent associated with 29 and 31 kDa proteins that are predomina ntly associated with mIgD (see accompanying paper). Amino acid sequenc ing of p32 and p37 identified p32 as mouse prohibitin; this was corrob orated by Western blot analysis with antibodies specific for rat prohi bitin. p37 is a newly discovered protein. cDNA clones for both protein s were isolated and sequenced. The deduced amino acid sequence of p32 is identical to that of rat prohibitin. p37 is highly homologous to p3 2. Since prohibitin was identified as an inhibitor of cell proliferati on, its association with mIgM, but not mIgD, could explain the differe nt biological events elicited after engagement of each receptor.