A regulatory sequence (also called a regulatory region or a regulatory area) is a segment of DNA where regulatory proteins such as transcription factors bind preferentially. These regulatory proteins bind to short stretches of DNA called regulatory regions, which are appropriately positioned in the genome, usually a short distance 'upstream' of the gene being regulated. By doing so, these regulatory proteins can recruit another protein complex, called the RNA polymerase. In this way, they control gene expression and thus protein biosynthesis.
Regulatory sequences can also be found in messenger RNA, but they are generally not as well studied as those in DNA. They may be bound by RNA-binding proteins or RNAs (e.g. miRNAs).
Research to find all regulatory regions in the genomes of all sorts of organisms is under way.  Conserved non-coding sequences often contain regulatory regions, a