In a second transgenic mouse line , an enhancer region , which binds to thyroid transcription factor 1 , retinoic acid receptor , signal transducers and activators of transcription 3 , and nuclear receptor coactivators ( SRC 1 , ACTR , TIF 2 , and CBP / p300 ) , was deleted from the hSP B 1 . 5 kb lacZ gene . ^^^