A SURROGATE 15-KDA JC-KAPPA PROTEIN IS EXPRESSED IN COMBINATION WITH MU-HEAVY-CHAIN BY HUMAN B-CELL PRECURSORS

A novel kappa protein, encoded by a germline JC kappa transcript, is expressed by normal and leukemic human B cell precursors. The transcript displays an open reading frame initiated by a non-AUG codon, and predicts a 15 kDa molecule which could be readily confirmed by in vitro translation. Cellular expression was demonstrated by immunofluorescence. precipitation and Western blotting. Furthermore, 2-D gel electrophoresis revealed that germline JC kappa can covalently associate with Ct heavy chain at the surface of pre-B cells. We therefore propose that during B cell lymphopoiesis, two alternative pathways could be operative in which mu heavy chain can either associate with lambda 5 or germline JC kappa.