Identification of the major immunoglobulin heavy chain poly A+ RNA in murine lymphoid tissue

Total cellular Poly A+ RNA from TEPC15 myeloma and murine lymphoid tissues was analyzed by denaturing agarose gel electrophoresis and Northern blot hybridization to specific heavy chain constant region cDNAs; mu, gamma 2b and alpha RNA species were identified in each of the tissues and in the IgA producing TEPC15 myeloma. In total Poly A+ RNA from TEPC15 myeloma, alpha-cDNA hybridized predominantly to a 2.3 kb RNA species; 11.5 and 4.1 kb RNA species were evident as well. Successive hybridization of the same RNA to mu- and gamma 2b-specific cDNAs demonstrated the presence of both mu and gamma 2b specific RNA species with electrophoretic mobilities apparently identical to the 11.5 and 2.3 kb RNA species identified by alpha-specific hybridization. These data establish the presence of Poly A+ RNA species containing alpha, mu, and gamma 2b sequences in TEPC15 cells and suggest the transcription of RNA from both CH-containing chromosomes in TEPC15 myeloma (one chromosome in the TEPC15 cell line contains all the CH genes while the other chromosome has deleted all CH genes except alpha). In total Poly A+ RNA from normal mouse tissues (Peyer's patch and spleen) all three cDNA probes hybridized predominantly to an 11.5 kb RNA species. Primer extension experiments demonstrated that alpha cDNA could prime for the synthesis by reverse transcriptase of gamma 2b DNA when Peyer's patch Poly A+ RNA was used as the template. This suggests the existence of a single transcript containing alpha and gamma 2b sequences. Murine lymphoid tissues contained putative mRNAs for mu, gamma 2b and alpha heavy chain proteins, whereas TEPC15 myeloma polysomal Poly A+ RNA contained only alpha mRNA.