sigma70

Sigma70 refers to the primary sigma factor subunit of bacterial RNA polymerase. Sigma factors are essential proteins that play a crucial role in the initiation of transcription, the process by which genetic information from DNA is copied into RNA. Sigma70, also known as the RpoD protein in E. coli, is the most abundant sigma factor in many bacterial species and is responsible for directing RNA polymerase to recognize and bind to promoter sequences upstream of genes that are constitutively expressed or involved in housekeeping functions. These promoters are characterized by specific DNA sequences, typically a -10 element (Pribnow box) and a -35 element, which are recognized by different domains of the sigma70 subunit. Without sigma70, RNA polymerase would bind to DNA non-specifically and transcription initiation would be inefficient. The binding of sigma70 to the core RNA polymerase enzyme forms a holoenzyme, which is the active form capable of initiating transcription. After transcription initiation, the sigma70 subunit typically dissociates from the core enzyme, allowing the polymerase to proceed with elongation of the RNA transcript. The regulation of sigma70 levels and its availability is critical for bacterial growth and adaptation to various environmental conditions.