Production of RNA for secreted immunoglobulin μ chains does not require transcriptional termination 5′ to the μm exons

Abstract

The mouse immunoglobulin μ gene encodes both secreted and surface-bound μ heavy chains produced by cells of the B lymphoid series. Transcripts of the μ gene are processed into μ mRNA species which differ at their 3′ termini, bearing either 'μS' or 'μM' segments, distinguishing secreted and cell-membrane-bound μ polypeptides1-3. During maturation of surface IgM-bearing B cells to IgM-secreting plasma cells, both the total amount of μ mRNA and the ratio of μS to μM-terminated mRNA increase greatly1,3,4. Two possible mechanisms for the developmental regulation of 3 RNA processing cannot yet be distinguished. One mechanism would yield the μS terminus by specific cleavage of a common presursor tr..