Bacterial and eukaryotic regulatory regions compared. (a) Bacterial promoters are usually regulated by only one or two transcription factors, and their binding sites are typically near, or overlap, the promoter. (b) Eukaryotic genes, especially those of multicellular organisms, usually have numerous regulator-binding sites spanning a large region (sometimes more than 50 kbp) located upstream and/or downstream from the promoter, or even within the coding sequence of the gene itself (not shown).