Difficulty: Easy
Correct Answer: recognition of the transcriptional start sequence
Explanation:
Introduction / Context:
In bacteria, the RNA polymerase holoenzyme includes a σ factor that confers promoter specificity. Correctly assigning σ factor function is central to understanding promoter recognition and gene regulation in prokaryotes.
Given Data / Assumptions:
Concept / Approach:
σ factors recognize and bind promoter DNA, positioning the core enzyme at the correct transcription start site (TSS). After initiation, σ often dissociates, allowing elongation. Different σ factors target distinct promoter classes, enabling adaptive gene expression.
Step-by-Step Solution:
Identify the relevant stage: initiation of transcription.Assign σ role: promoter recognition and TSS selection.Therefore, σ recognizes transcriptional start sequences.
Verification / Alternative check:
Mutations in −10/−35 elements reduce σ-dependent binding and initiation, confirming its role in start-site recognition.
Why Other Options Are Wrong:
Common Pitfalls:
Mixing translation signals with transcription signals due to similar “start/stop” wording. Keep the processes distinct.
Final Answer:
recognition of the transcriptional start sequence
Discussion & Comments