The E1A enhancer region contains a repressor element that responds to IFNs.

<p>(A) Schematic view of the left end of the Ad5 genome is shown at the top including the inverted terminal repeat (ITR), E1A enhancer region, CAAT and TATA boxes, and transcription start site (TSS). Shown below are the GABP and E2F binding sites in the E1A enhancer and the boundaries of enhancer element II. E1A enhancer region deletion mutants are depicted below the schematics. (B) Sequence of Ad5 nt 250–320 including the E2F and GABP binding sites and flanking sequences and the location of linker scanning mutants generated in this region (Ad5-mut1–mut3). The black rectangles with letters indicate nucleotide substitutions. The yellow rectangle indicates the boundaries of the IFN-induced repressor site delimited by the deletions mutants in (A). (C) HDF-TERT cells were treated with IFNs or left untreated for 24 hr and then infected with the mutant viruses illustrated in (A) and (B), as well as the corresponding parent virus (<i>dl</i>309, <i>in</i>340 and Ad5-WT). E1A protein levels were examined at 48 hr post-infection by Western blot. α-tubulin was used as a loading control for the samples. (D) NHBEC cells were pretreated with IFNs or left untreated for 24 hr and then infected with Ad5-WT at 100 virus particles/cell and E1A protein levels were analyzed at 24 hr post-infection by Western blot. α-Tubulin was used as a loading control.</p>