Analysis of immunoglobulin heavy chain delta transcription termination in the production of delta S or delta M mRNA.

mRNA encoding secreted immunoglobulin is synthesized either by termination of transcription 3' to secreted terminus sequences and 5' to the membrane terminus sequences or by cleavage of a pre-mRNA transcript containing both secreted and membrane sequences at the appropriate polyadenylation site 5' to the membrane sequences. In vitro "run-on" transcription analysis was used to examine the delta transcription termination patterns in resting membrane IgD expressing B lymphocytes, in KWD2, an IgD-secreting hybridoma, and in TEPC 1017, an IgD-secreting plasmacytoma. In resting B cells, transcription terminated in a region 4 to 7 kilobases 3' to the delta M exons. Transcription in the secreting cells continued through the delta M exons, but terminated at more upstream sites. Additionally, an increased loading of polymerases in the region of the delta S exon and its 5' flanking sequence was detected in the secreting cells and was particularly pronounced in TEPC 1017. It is hypothesized that this peak correlates with high delta S mRNA production.