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Transcriptional initiator elements and TATA elements are functionally similar, in that both can act in concert with a Sp1-dependent activator element to direct high levels of accurately initiated transcription. In this study, we have used in vitro transcription experiments to elucidate the relative activities of TATA and initiator. By varying the locations of TATA and initiator elements within a simple promoter, we compared their abilities to localize transcription start sites and to mediate transcriptional activation by Sp1. In addition, we addressed the contributions of initiator and TATA towards determining the direction of transcription from a promoter. Finally, we addressed the prevalence of initiator elements by analyzing the start site regions of several genes. We found that many of these regions possess initiator activity, although an initiator consensus sequence could not be defined. Taken together, the data presented suggest that an initiator is a common element that can influence the direction of transcription as well as the location of a transcription start site. However, in general, an initiator was incapable of altering these activities of a TATA box within a promoter containing both core elements.
O'Shea-Greenfield et al. (Wed,) studied this question.