Question

Listed below are sigma subdomains followed by its function. Which of the following pairings has an incorrect function assigned?

A. Extended helix 2.3/2.4; recognizes and melts -10 element

B. H-T-H 1.1; blocks the exit pore of RNA

C. Hairpin 3.2; keeps contact with the first nucleotide of the nascent RNA until abortive cycling or elongation occurs

D. H-T-H 4.2; recognizes -35 element

Answer 1

The incorrect function is assigned to pairing B. H-T-H 1.1. This sigma subdomain does not block the exit pore of RNA but rather stabilizes the sigma factor by interacting with the core RNA polymerase.

Step-by-step explanation:

The pairing that has an incorrect function assigned is B. H-T-H 1.1; it is not responsible for blocking the exit pore of RNA. The function of H-T-H (helix-turn-helix) motif 1.1 is to interact with the core RNA polymerase to stabilize the sigma factor and does not block the exit pore of RNA. The sigma factors are essential for the initiation of transcription in bacteria, recognizing specific promoter regions on the DNA and facilitating the binding of RNA polymerase to the DNA.

Sigma factors have subdomains with specific functions: for example, sigma subdomain 4.2 is known to recognize the -35 element on the DNA during the initiation of transcription, not the H-T-H 1.1. Therefore, while the other pairings mentioned correctly associate sigma subdomains with their respective functions in interacting with the core RNA polymerase and recognizing DNA elements, pairing B associates an incorrect function with H-T-H 1.1.