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Nat Immunol. 2003 May;4(5):442-51.

R-loops at immunoglobulin class switch regions in the chromosomes of stimulated B cells.

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USC Norris Comprehensive Cancer Center, Room 5428, University of Southern California Keck School of Medicine, 1441 Eastlake Avenue, MC 9176, Los Angeles, CA 90033, USA.


The mechanism responsible for immunoglobulin class switch recombination is unknown. Previous work has shown that class switch sequences have the unusual property of forming RNA-DNA hybrids when transcribed in vitro. Here we show that the RNA-DNA hybrid structure that forms in vitro is an R-loop with a displaced guanine (G)-rich strand that is single-stranded. This R-loop structure exists in vivo in B cells that have been stimulated to transcribe the gamma3 or the gamma2b switch region. The length of the R-loops can exceed 1 kilobase. We propose that this distinctive DNA structure is important in the class switch recombination mechanism.

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