Which factor confers RNA polymerase (RNAP) with promoter specificity?

The sigma factor is crucial for RNA polymerase to recognize specific promoter sequences in DNA. It serves as a guiding protein that associates with the core RNA polymerase enzyme (composed of alpha, beta, beta prime, and omega subunits) to form a holoenzyme capable of initiating transcription.

The sigma factor plays a key role by binding to the promoter region of the gene, specifically recognizing and interacting with consensus sequences found in the -10 (Pribnow box) and -35 regions of prokaryotic promoters. This specific interaction allows the RNA polymerase to properly align itself with the DNA template at the start of transcription, ensuring that the correct gene is expressed.

Without the sigma factor, RNA polymerase would not be able to differentiate between various promoters, leading to a lack of specificity in transcription initiation and potentially resulting in errors in gene expression. Thus, the sigma factor is essential for promoter specificity, enabling the transcription machinery to initiate the correct genes in response to various cellular conditions.