Generating HS2 core deletion. (A) Strategies for the murine β-globin LCR 5′HS2 deletions. (i) Schematic representation of HS2 and the homologous recombination (HR)-targeting construct with the CMV-HyTK gene flanked by 2 inverted loxP sites (arrows) replacing the 5′HS2 full site. (ii) Structure of the HR product with the RMCE site replacing the full 5′HS2. (iii) RMCE constructs. (iv) RMCE products showing the full deletion and the core deletion with the 5′HS2 flanks in their normal or inverted orientation. (B) Sequence comparison of the human and mouse 5′HS2 core deletions, including the binding sites of transcription factors most likely to be bound to the core.⁷