CreERT2 activity was induced by 4-hydroxytamoxifen to facilitate Cre-mediated insertion of the PAIR4 sequences into the lox71 site at the deletion point (117,126,667/116,237,220; mm9, Chr.12) of the Ightm4.2Mbu allele. The rox-flanked Actb-Bsd expression cassette was deleted after germline transmission. (J:341427)