What role does the sigma factor of RNA polymerase have in transcription?

• A. It adds a 5' cap to the newly synthesized mRNA.
• B. It recognizes and binds to promoter sequences, guiding RNA polymerase to the correct initiation site.
• C. It catalyzes the formation of phosphodiester bonds between ribonucleotides.
• D. It unwinds the DNA double helix ahead of the transcription bubble.

Answer: (B)

Verified step by step guidance

1. Understand the process of transcription: Transcription is the synthesis of RNA from a DNA template. RNA polymerase is the enzyme responsible for this process, and it requires specific factors to initiate transcription accurately.
2. Learn about the sigma factor: The sigma factor is a protein subunit of RNA polymerase in prokaryotes. It plays a crucial role in guiding RNA polymerase to the correct initiation site for transcription.
3. Explore the role of the sigma factor in promoter recognition: The sigma factor recognizes and binds to specific DNA sequences called promoters. Promoters are regions upstream of the gene that signal where transcription should begin.
4. Understand how the sigma factor helps RNA polymerase: Once the sigma factor binds to the promoter, it helps RNA polymerase position itself correctly at the transcription start site. This ensures that RNA synthesis begins at the right location.
5. Clarify the sigma factor's role in transcription initiation: After RNA polymerase is properly positioned, the sigma factor dissociates, allowing the core RNA polymerase enzyme to proceed with elongating the RNA strand by catalyzing the formation of phosphodiester bonds between ribonucleotides.