Cis-acting regulatory sequences promote high-frequency gene conversion between repeated sequences in mammalian cells

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Oxford University Press

RESUMO

In mammalian cells, little is known about the nature of recombination-prone regions of the genome. Previously, we reported that the immunoglobulin heavy chain (IgH) μ locus behaved as a hotspot for mitotic, intrachromosomal gene conversion (GC) between repeated μ constant (Cμ) regions in mouse hybridoma cells. To investigate whether elements within the μ gene regulatory region were required for hotspot activity, gene targeting was used to delete a 9.1 kb segment encompassing the μ gene promoter (Pμ), enhancer (Eμ) and switch region (Sμ) from the locus. In these cell lines, GC between the Cμ repeats was significantly reduced, indicating that this ‘recombination-enhancing sequence’ (RES) is necessary for GC hotspot activity at the IgH locus. Importantly, the RES fragment stimulated GC when appended to the same Cμ repeats integrated at ectopic genomic sites. We also show that deletion of Eμ and flanking matrix attachment regions (MARs) from the RES abolishes GC hotspot activity at the IgH locus. However, no stimulation of ectopic GC was observed with the Eμ/MARs fragment alone. Finally, we provide evidence that no correlation exists between the level of transcription and GC promoted by the RES. We suggest a model whereby Eμ/MARS enhances mitotic GC at the endogenous IgH μ locus by effecting chromatin modifications in adjacent DNA.

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