Describes the function of the sigma factor in prokaryotic transcription

A sigma factor is a protein that initiates the transcription in prokaryotic. Sigma factor function is to control the gene expression and raises the specificity for the promoter sites. Sigma factor initiates the transcription in prokaryotes such as bacteria by binding core RNA polymerase at the genes promoter sites that form RNAP holoenzyme which recognizes the promoter and then the transcription initiated.