Multiple Immunoglobulin Heavy-Chain Gene Transcripts in Abelson Murine Leukemia Virus-Transformed Lymphoid Cell Lines

Lymphoid cells transformed by Abelson murine leukemia virus (A-MuLV) contain three classes of RNA transcripts from immunoglobulin mu genes. P mu-mRNAs (productive) correspond to the normal 2.7-kilobase (kb) membrane (mu m) and 2.4-kb secreted (mu s) mu mRNA species both in size and coding capacity and occur at approximately equal abundance in most mu-positive (pre-B-like) A-MuLV transformants. A mu-mRNAs (aberrant) generally fall into one of two categories--aberrantly small 2.3-kb mu m and 2.0-kb mu s mRNAs which encode aberrantly small mu polypeptide chains, or normal-sized, V H-containing mu RNAs which do not encode immunologically identifiable mu polypeptide chains. In one case, the latter type of A mu-mRNA was demonstrated to result from an in-phase termination codon in the D segment of the mu mRNA. Also, most, if not all, A-MuLV transformants express members of a 3.0 to 1.9-kb set of C mu-containing, but V H-negative S mu-RNAs (for sterile), the expression of which may occur simultaneously with but independently of P mu-mRNAs or A mu-mRNAs. The S mu-RNA sequences do not encode immunologically identifiable mu chains and can be produced by cells with unrearranged heavy-chain alleles, such as T-lymphocytes, although the structure of the S mu-RNAs from T-lymphoid cells appears to be different from that of B-lymphoid cell S mu-RNAs. Certain A-MuLV transformants also express gamma-RNA sequences that are probably analogous to the three different forms of mu RNA. These data support the concept that heavy-chain allelic exclusion, like that of light chains, is not mediated by control at the DNA or RNA levels but is probably a consequence of feedback control from cytoplasmic mu chains.