2 NEW PROTEINS PREFERENTIALLY ASSOCIATED WITH MEMBRANE IMMUNOGLOBULIN-D

The IgM and IgD classes of antigen receptor can perform different func tions on B cells. However, so far no class-specific components communi cating with the cytoplasm have been found in the two antigen receptors . We have employed a new biotinylation protocol to search for intracel lular membrane Ig-associated proteins. Here we describe two proteins o f 29 and 31 kDa that are associated with membrane IgD and to some exte nt with membrane IgM. The membrane IgM molecule is associated specific ally with three proteins of 32, 37 and 41 kDa. The purification and se quencing of the two mIgD-associated proteins revealed that they are no vel proteins which are related to each other. These proteins may be th e missing link between the antigen receptor and the cytoskeleton and m ay contribute to functional differences between membrane IgM and membr ane IgD.