THE NOVEL VARIANTS OF MB-1 AND B29 TRANSCRIPTS GENERATED BY ALTERNATIVE MESSENGER-RNA SPLICING

The Ig-alpha/Ig-beta heterodimers encoded by mb-1 and B29 genes, respe ctively, are crucial for the constitution of the B-cell receptor (BCR) . We report here novel variants of mb-1 and B29 transcripts produced b y alternative mRNA splicing, The proteins encoded by these variants ar e predicted to conserve transmembrane and cytoplasmic portions of Ig-a lpha and Ig-beta but lack a part of the extracellular portions contain ing cysteine residues which are required for intramolecular and interm olecular S-S bonds, Transfection studies revealed that the variant mb- 1 and B29 did not contribute to the BCR expression on cell surfaces, A lthough peripheral B cells contain small amounts of the variant mb-1 a nd B29 transcripts, treatment with an anti-IgM antibody, LPS or IL-4 i nduces a significant increase in amounts of the variant transcripts, T hese observations suggest that B-cell activation induces alternative s plicing of mb-1 and B29 transcripts which encode proteins unable to co nstitute the BCR.