A novel 34-kd protein co-isolated with the IgM molecule in surface IgM-expressing cells.

Abstract

Plasmacytoma cells, transfected with a vector encoding a membrane‐bound IgM molecule, do not show cell surface IgM expression, although complete IgM molecules are assembled intracellularly. The isolation of a surface IgM‐positive variant allowed us to analyse molecular requirements of surface IgM expression. Only in surface IgM‐positive cells, a 34‐kd protein (B34) was found to be associated with IgM. B34 is a glycoprotein which forms a disulphide‐linked homodimer. The surface IgM‐positive variant cell line expressing B34 also contains transcripts of the pre‐B and B cell specific mb‐1 gene. The data are discussed in the context of a possible IgM‐antigen receptor complex.