ABSTRACT
The level of transcription directed by the basal transcriptional complex binding at the promoter is greatly enhanced by the binding of other constitutively expressed factors to so-called upstream promoter elements (UPEs), which are usually located immediately upstream from the promoter itself. Although the nature of the UPEs varies between different genes, very many genes contain either or both the CCAAT box that binds a variety of different transcription factors and a GC-rich sequence that binds the constitutively expressed transcription factor Spl. Although most constitutively expressed or regulated transcription factors act by activating the transcription of specific genes, it is also possible for transcription to be specifically inhibited by the action of a transcription factor. The cell type-specific or inducible expression of specific proteins that is commonly observed in higher eukaryotes is dependent on the cell type-specific or inducible transcription of the corresponding genes encoding these proteins.
