GERMLINE TRANSCRIPTS OF THE MURINE IMMUNOGLOBULIN GAMMA-2A GENE - STRUCTURE AND INDUCTION BY IFN-GAMMA

The switch in expression by B cells from IgM to IgG, IgE, or IgA is ac complished by a DNA deletion. The deletion event is regulated, in that specific cytokines direct the B cell to switch to one, or sometimes t wo, of the six possible murine heavy chain genes. Prior to switch reco mbination, cytokine treatment also induces the transcription of the co nstant, switch, and upstream regions of the targeted heavy chain. Much evidence indicates that IFN-gamma directs switch recombination to the murine gamma2a gene. By developing probes specific for the gamma2a ge ne, we demonstrate that IFN-gamma increases germline transcription of this gene in both normal 8 cells and in the 18.81.A20 pre-B lymphoma. We have obtained cloned copies of three different germline gamma2a tra nscripts, each with a different donor splice site. We have also locate d the 5' ends of these transcripts. The vast majority of the germline gamma2a transcripts have a long first exon (> 700 bp), consistent with observations by Severinson and her colleagues.