In vitro transcription systems are used to identify promoter signals and factors that control transcription in eucaryotic systems. These systems accurately initiate transcription from a wide variety of promoters. Under modified assay conditions, expression of the adenovirus IVa2 gene is readily observed in vitro. This adeno gene, like the SV40 late genes, lacks a TATA box upstream from the 5' start site. By constructing a series of upstream deletion mutations, two upstream domains have been identified that control this gene. The distal domain only functions when covalently closed DNA is used as a template and contains within it two separate regions. One is believed to function as the entry site for RNA polymerase II while the second region inhibits transcription of the IVa2 gene.
