In bacteria and eukaryotes, transcription is regulated by proteins which bind to the specific sites and modulate the activities. These sites are located on the chromosome, and they are a cluster of gene sequences known as operons. Operons are under the control of a single promoter, and can be induced/repressed or may work consistently all the time. Main regulation of transcription occurs by rearrangement of histone proteins, which are located on the chromosome itself. These proteins may leave the desired gene sequence inaccessible for further operations.
