Map of the human β-globin cluster–containing BAC. A 100-kb HindIII fragment containing the human β-globin cluster was generated by a partial digest of the 180-kb PAC 4396 and subcloned into the 7.4-kb pBeloBAC 11 vector to create BAC 4396-44. The BAC 4396-44 insert was subsequently released from the vector by aNotI digest, isolated by PFGE, and microinjected into fertilized mouse eggs or transfected into ES cells.