Induction of RNA-stabilized DMA conformers by transcription of an immunoglobulin switch region

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Abstract
A DELETIONAL DNA rearrangement is associated with immunoglobulin class switching from IgM to IgG, IgA or IgE (reviewed in ref. 1). This recombination occurs in immunoglobulin switch regions, which are complex, highly repetitive regions of DNA. As switch regions become transcriptionally active2,3 just before switch recombination, analysis of the behaviour of these sequences during transcription could elucidate the mechanism of switch recombination. Here, we report that transcription of a supercoiled plasmid containing the murine IgA switch region (Sα)leads to a loss of superhelical turns. The resulting series of less supercoiled plasmids is stabilized by RNA-DNA hybrids formed by the nascent RNA transcripts, which remain base-paired with their DNA templates.