In genetics, an enhancer is a short (50-1500 bp) region of DNA that can be bound by proteins (activators) to activate transcription of a gene. These proteins are usually referred to as transcription factors. Enhancers are generally cis-acting, located up to 1 Mbp (1,000,000 bp) away from the gene and can be upstream or downstream from the start site, and either in the forward or backward direction. There are hundreds of thousands of enhancers in the human genome.