Expression vectors for bacterial overproduction In a protein overexpression plasmid designed for bacteria, the promoter driving the cloned gene is typically:

Introduction / Context:
Expression vectors used to overproduce proteins in bacteria rely on powerful, well-characterized bacterial promoters to achieve high transcription levels and tight control. Selecting the correct promoter type is critical for yield, solubility, and host viability.

Given Data / Assumptions:

• Goal: overproduce a heterologous protein in a bacterial host.
• Promoters must be recognized by bacterial RNA polymerase (or phage polymerases expressed in bacteria).
• Tight regulation is often needed to avoid toxicity.

Concept / Approach:
Common bacterial expression systems use strong promoters such as T7 (driven by T7 RNA polymerase in hosts like BL21(DE3)), tac/trc (hybrids of trp and lac), lac, or arabinose-inducible araBAD. These are specifically optimized for bacterial machinery and frequently inducible for control. Using a gene’s native promoter is uncommon for overexpression because it may be weak or poorly regulated in the host. Cross-kingdom promoter compatibility is generally poor without engineered hybrid systems.

Step-by-Step Solution:
Identify the host: bacteria require bacterial or phage-derived promoters recognized in bacteria.Recognize the need for strength and regulation.Select the option describing a bacterial (often inducible) promoter as standard.

Verification / Alternative check:
Widely used systems (e.g., T7/lac operon control in BL21(DE3)) exemplify this approach and are standard in molecular cloning labs and industry.

Why Other Options Are Wrong:

• Dual expression in bacteria and mammalian cells with the same promoter is atypical.
• “Not regulated” is inaccurate; most systems are inducible.
• Native promoters often underperform and are less controllable.
• Eukaryotic TATA promoters are not directly functional in bacteria without extensive engineering.

Common Pitfalls:
Forgetting the role of host-specific polymerases; assuming a native promoter is sufficient for high-level expression.

Final Answer:
A bacterial promoter (often strong and regulatable, e.g., T7, tac, trc, lac, araBAD).