Burkitt's lymphoma cell lines producing truncated mu immunoglobulin heavy chains lacking part of the variable region

Burkitt's lymphoma cell lines Ly91, Ly47 and JBL2 contained intracytoplasmic mu chains without light chains and variably expressed membrane mu chains. All three cell lines produced similarly truncated heavy chains with an apparent molecular mass of 64 kDa instead of the normal 74 kDa. Both the intracellular and secreted forms of the mu chains were similarly truncated. The membrane and the secreted forms of mu mRNAs were shorter than normal. The cDNAs contained a leader sequence, followed by about one third of a variable region (VH), then by the constant region (C mu). Interruption of the variable region took place near the end of the framework region 1 (FR 1) in Ly 47 and JBL2, and within the complementarity determining region 1 (CDR1) in Ly91. In the three lines, the joining between VH and C mu maintained the normal open reading frame throughout the variable and constant regions.