DNA Transcription Promoter Regions The promoter regions for RNA polymerases I and II are located upstream of the start site, but the promoter for polymerase III is oddly located down stream. One key difference between prokaryotic and eukaryotic transcription is that eukaryotic polymerases are unable to recognize promoter regions. They have no direct parallel to the sigma subunit of their prokaryotic counterpart. Instead, eukaryotic polymerases depend on other proteins that bind to the promoter regions and then recruit the RNA polymerases to the correct spots. Unlike prokaryotic promoters, eukaryotic promoter regions do not have a "canonical sequence". They do, however, have more flexible modular elements. The polymerase II promoter, for example, has a number of traditional sequences that can appear either in tandem or alone. At the least, polymerase II promoters must have either a "TATA box", a region approximately 25 base pairs upstream from the start-site with the sequence TATAAAA, or an "initiator element". The
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