enhancer

1. A substance or object that increases a chemical activity or a physiological process. 2. A eukaryotic DNA sequence (also found in some eukaryotic viruses) which increases the transcription of a gene. Located up to several kbp, usually (but not exclusively) upstream of the gene in question. In some cases can activate transcription of a gene with no (known) promoter. Synonyms: enhancer element; enhancer sequence. 3. A major or modifier gene that increases the rate of a physiological process.