Eukaryotic mRNA processing — The mature mRNA from which source would be expected to carry a 3′ poly(A) tail?

Introduction:
Polyadenylation is a hallmark of most eukaryotic mRNAs, enhancing stability, nuclear export, and translation. This question distinguishes eukaryotic mRNA processing from bacterial and phage transcripts.

Given Data / Assumptions:

• Eukaryotic pre-mRNAs are typically 5′-capped, spliced, and 3′-polyadenylated.
• Bacterial and bacteriophage mRNAs usually lack long 3′ poly(A) tails that function like eukaryotic poly(A); short polyadenylation in bacteria often marks decay.
• Human insulin is a eukaryotic gene expressed in human cells.

Concept / Approach:
Identify the organismal origin of the mRNA. Eukaryotic mRNAs (e.g., human insulin mRNA) receive a poly(A) tail via poly(A) polymerase after cleavage at a consensus site; bacterial/phage transcripts generally do not have this eukaryotic-style modification.

Step-by-Step Solution:

Verification / Alternative check:
mRNA isolation protocols (oligo-dT selection) enrich eukaryotic polyadenylated transcripts such as insulin mRNA, confirming the presence of a poly(A) tail.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming all RNAs have poly(A); conflating bacterial polyadenylation (RNA turnover) with eukaryotic stabilization.

Final Answer:
Human insulin mRNA.