passages.id: split_4_validation_42_passage
passages.type: progene_text
passages.text: We now report that differentiation represses SRE serum inducibility using nontransformed cells transiently transfected with pjunB SRE thymidine kinase / chloroamphenicol acetyltransferase ( SREtk / CAT ) or pc-fos SREtk / CAT containing an intact SRF - binding domain .