Analysis of mu-specific mRNA in the B cell tumor line, BCL1, shows that the cells contain predominantly mRNA for mu chain of membrane-bound immunoglobulin M (IgM) (2.7 kb, mu m mRNA). Stimulation of the cells to Ig secretion by lipopolysaccharide (LPS) results in a 6-12 fold increase in amount of mRNA for the mu chain of secreted IgM (2.4 kb mu s mRNA). The increase in mu s mRNA is accompanied by a 3-4-fold increase in mu m mRNA. The rate of mu chain synthesis of membrane IgM in LPS-stimulated cells is, however, reduced by at least twofold, suggesting that both transcriptional and translational regulatory events are involved in the induction of B lymphocytes to secretion.

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