Programmed DNA recombination in mammalian cells occurs predominantly in a directional manner.While random DNA breaks are typically repaired both by deletion and by inversion at approximately equal proportions,V(D)J and class switch recombination (CSR) of immunoglobulin heavy chain gene overwhelmingly delete intervening sequences to yield productive rearrangement.What factors channel chromatin breaks to deletional CSR in lymphocytes is unknown.Integrating CRISPR knockout and chemical perturbation screening we here identify the Snf2-family helicase-like ERCC6L2 as one such factor.We show that ERCC6L2 promotes double-strand break end-joining and facilitates optimal CSR in mice.At the cellular levels,ERCC6L2 rapidly engages in DNA repair through its C-terminal domains.Mechanistically,ERCC6L2 interacts with other end-joining factors and plays a functionally redundant role with the XLF end-joining factor in V(D)J recombination.Strikingly,ERCC6L2 controls orientation-specific joining of broken ends during CSR,which relies on its helicase activity.Thus,ERCC6L2 facilitates programmed recombination through directional repair of distant breaks.
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