ABSTRACT
Many genes are active in all cells but some are transcribed only in specific cell types, at specific times and/or only in response to specific external stimuli. Transcriptional regulation in a eukaryotic cell is mediated by transcription factors, other than the general transcription factors, which recognize and bind to short regulatory deoxyribonucleic acid (DNA) sequences associated with the gene. Activator proteins usually have at least two distinct domains of protein structure, a DNA-binding domain that recognizes the specific DNA sequence to bind to, and an activation domain responsible for bringing about the transcriptional activation by interaction with other transcription factors and/or the ribonucleic acid polymerase molecule. Many transcription factors bind to control elements within a few hundred base-pairs of the protein-coding gene being regulated. An enhancer is typically 100–200 bp long and contains several sequence elements that act together to give the overall enhancer activity.
