Which subunit of RNA polymerase holoenzyme is responsible for promoter recognition?

The sigma subunit of RNA polymerase holoenzyme plays a critical role in initiating transcription by recognizing and binding to specific promoter sequences on the DNA. This recognition is essential for the proper positioning of the RNA polymerase at the transcription start site. The sigma factor helps the enzyme distinguish between different promoter sequences, allowing for precise initiation of transcription at the correct location.

This subunit is part of the holoenzyme complex and can be replaced or altered to allow RNA polymerase to recognize different promoters in response to cellular conditions or developmental stages. The functionality of the sigma subunit in promoter recognition is fundamental to the regulation of gene expression, as it helps dictate which genes are expressed under specific circumstances.

The other subunits of RNA polymerase contribute to the overall enzymatic activity and stability of the holoenzyme, but they do not have the specific role of recognizing promoters during the initiation of transcription.