Sigma subunit

Sigma subunit σ is a subunit located on RNA polymerase. When combined with a sigma factor, it recognizes the promoter used in transcription for bacteria. Its alpha helix interacts with a sequence call Pribnow box or -10 region on the promoter site.

Sigma subunit initiates transcription and directs the CORE to transcribe specific genes by
 * 1. Recognizing promoters (promoter: specific DNA sequences in the upstream region of a gene indicating the point of initial transcription)
 * 2. Cause the CORE to bind tightly to a promoter