Sigma factor is the name of the protein and it helps RNA polymerase to recognize promoter.
Explanation:
RNA polymerase is the enzyme which helps in the transcription of DNA duplex. In bacteria, a protein called sigma factor is present in RNA polymerase which is responsible for the initiation of transcription.
The sigma factors gives the ability to RNA polymerase to recognize the promoter sequence. If the sigma factor is not present in RNA polymerase than this enzyme can not distinguish between promotor and other sequences.
So the sigma factor increases the affinity of RNA polymerase towards promoter and helps in initiation of the transcription. Sigma factor gets released from the core enzyme when the chain reaches 8-9 bases.
