Of the five early adenovirus promoters, the early region 3 (E3) promoter is one of the most strongly induced by the E1A protein. To identify cellular proteins involved in both the basa1 and ElA-induced transcriptional regulation of the E3 promoter, ONase I footprinting using partially purified Hela cell extracts was performed. Four regions of the E3 promoter serve as binding domains for cellular proteins. These regions are found between -156 to -179 (site IV), -83 to -103 (site III), -47 to -67 (site II), and -16 to -37 (site I), relative to the start of transcription. Examination of the DNA sequences in each binding domain suggests that site III likely serves as a binding site for activator protein 1 (AP-1), site II for the cyclic AMP regulatory element binding protein (CREB), and site I for a TATA binding factor. The factors binding to either site II or III were sufficient to stabilize binding to the TATA sequence (site I). Mutagenesis studies Indicated that both sites II and III, in addition to site I, are needed for complete basal and ElA-induced transcription. These results suggest that multiple cellular factors are Involved in both the basal and EIA-induced transcriptional regulation of the E3 promoter, and that either of two upstream regions are capable of stabilizing factor binding to the TATA sequence.
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