Operon

The promoter is one of the gene expression control units. According to the operon model they include:


Regulator gene - a gene that codes for a repressor protein molecule. The repressor molecule binds to the operator and prevents RNA polymerase from binding to the promoter. Promoter - a short sequence of DNA where RNA polymerase first attaches when a gene is to be transcribed. Operator - a short sequence of DNA where the repressor binds, preventing RNA polymerase from attaching to the promoter. In addition, the part of chromosome (in eukaryotic cells) containing the gene must first decompact to form a "chromosome puffs" before the beginning of transcription.