A core promoter element downstream of the TATA box. (A) Sequence of the Adenovirus E4 (AdE4) promoter, both positive and negative strands (nucleotides -51 to +12). The TATA box, as determined experimentally, is shown in bold on the positive strand. The randomized bases (N) downstream of the TATA box (bold) are shown below.(B) Bandshift assay using the radiolabeled randomized library (Random) compared with the DNA recovered after seven rounds of selection (7th round). Free probe (FP) and TFIIB–TBP–DNA complex (T-B-DNA) are indicated. Two-hundred nanograms of hTBP and increasing amounts of hTFIIB (4, 20, and 100 ng) were included in the reaction. Below the autoradiograph, the data have been quantitated and graphed. (C) Forty-one different clones were sequenced after seven rounds of selection. The frequency of occurrence of each base within the randomized region is shown. Below, the consensus sequence derived from the selection is shown with the size of each letter reflecting the frequency (where >9) of the occurrence of the base at each position.