passages.id: split_8_test_652_passage
passages.type: progene_text
passages.text: Analysis of the E2F1 gene promoter showed that the - 146 to - 54 region was required for E2 - responsiveness in transient transfection assays , and subsequent deletion / mutation analysis showed that a single upstream GC - rich and two downstream CCAAT - binding sites were required for transactivation by E2 .