mRNA architecture In bacterial transcription, what is the nontranslated segment located between the transcription start site (+1) and the start codon of translation?

Introduction / Context:
mRNA molecules have regulatory regions that are not translated into protein. Understanding the leader (5′ UTR) helps explain ribosome binding, translational control, and mRNA stability. This is a core concept in gene expression and synthetic biology design of ribosome binding sites.

Given Data / Assumptions:

• We are focusing on the region downstream of +1 (transcription start) but upstream of the start codon (AUG/alternative).
• Prokaryotic mRNAs often include a Shine–Dalgarno site within the leader.
• The segment is transcribed but not translated.

Concept / Approach:

The 5′ UTR (leader sequence) contains elements that influence translation initiation, including ribosome binding sites, secondary structures, and regulatory protein or small RNA binding sites. The coding region begins at the start codon; the 3′ UTR (trailer) lies after the stop codon.

Step-by-Step Solution:

Verification / Alternative check:

Genome annotations label coding sequences (CDS) distinct from 5′ UTR, and functional studies show leader alterations change translation without altering coding sequence.

Why Other Options Are Wrong:

• Ending frame/trailer: These refer to 3′ regions after the stop codon.
• Reading frame/ORF: This is the translated coding region.
• Promoter −10: Lies upstream of +1 and is not part of the transcribed UTR.

Common Pitfalls:

• Equating transcription start with translation start—these are distinct events and positions.

Final Answer:

Leader sequence (5′ untranslated region / 5′ UTR)