(a) Schematic representation of the IgH locus of WT and of 8X-LexA binding element (LexA-BE) knocked-in CH12F3-2A cells. The a, b and c bars indicate the position of primers used for ChIP-qPCR in Fig. 1b. A protein in which the DNA-binding domain (DB) of LexA was tagged with 3X-FLAG and a nuclear localization signal (NLS) (FNLDD) was expressed in WT (FNLDD alone) and Sα-engineered (FNLDD- Sα-LexA) CH12F3-2A cells. 