Fig 1. Method for identifying non-canonical HR termination products in mammalian cells.

(A) Schematic of the HR reporter. Duplication of a blasticidin resistance cassette during LTGC allows expression of wt BsdR by splicing. Thus, I-SceI-induced STGCs are GFP⁺ and Bsd sensitive (BsdR^–), while I-SceI-induced LTGCs are GFP⁺ and Bsd resistant (BsdR⁺). Most LTGCs resolve as “GFP triplication” events, but a small fraction of LTGCs resolve by non-canonical mechanisms. Non-canonical LTGC termination products can be distinguished by the structure of the LTGC product, as shown. (B) Characterization of XRCC4^fl/fl and XRCC4^Δ/Δ Cre-treated HR reporter clones. Upper panel: Southern blotting, as described in Materials and Methods. Lower panel: western blotting for XRCC4 or for ß-tubulin loading control.