The M13 bacteriophage vector used to identify specific gene sequences (e.g., viral spike proteins) represents which type of expression system?

1. A

   Phage expression

2. B

   Bacterial expression

3. C

   Yeast expression

4. D

   Mammalian expression

Appeared in: INI-CET EXAM -2025

Explanation

• The M13 vector is a bacteriophage, which is a virus that specifically infects bacteria (in this case, E. coli).
• When a bacteriophage is used as a vehicle to carry and express a foreign gene within a host, the system is termed a phage expression system.
• This is distinct from other systems because the vector itself is a virus.
• A primary application is phage display, where the expressed protein (e.g., a viral spike protein) is presented on the phage's outer coat, making it useful for studying binding interactions and for antibody engineering.

Why Other Options Were Wrong

• Option B: While the phage uses a bacterial host (E. coli) for replication and protein synthesis, the vector itself is a phage, not a bacterial plasmid. Bacterial expression systems typically involve the direct transformation of bacteria with a plasmid vector.
• Option C: Yeast expression systems use yeast cells (e.g., Saccharomyces cerevisiae) as the host organism. Bacteriophages like M13 cannot infect yeast cells.
• Option D: Mammalian expression systems use mammalian cell lines as hosts. The M13 bacteriophage does not infect mammalian cells.

Related Visual

• Visual 1: Diagram: The life cycle of an M13 bacteriophage and its use in a phage display system. The visual should show the insertion of a foreign gene into the phage DNA, infection of an E. coli host, and the subsequent expression and display of the foreign protein on the new phage particles.

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Recombinant DNA Technology and Vector Types as background academic context rather than a clinical decision trigger.
• Phage display technology, which uses phage expression systems, is a powerful tool in medicine for discovering novel antibodies for therapeutic use against cancer and autoimmune diseases.
• It is also used in vaccine development and for identifying potential drug targets by screening vast libraries of proteins for specific binding interactions.
• What if the goal was to produce large quantities of a simple protein like insulin inside a cell? In that case, a bacterial expression system using a high-copy plasmid in E. coli would be the more common and efficient choice, making 'Bacterial expression' the correct answer in that context.

How to Approach the Question

• First, identify the core subject of the question, which is the 'M13 bacteriophage vector'.
• Break down the term: 'Bacteriophage' is a virus that infects bacteria. A 'vector' is a vehicle for carrying genetic material. An 'expression system' is the combination of a vector and a host used to produce a protein.
• Synthesize these parts: The system uses a phage virus to express a gene inside a bacterial host.
• Evaluate the options based on this understanding. 'Phage expression' is the only option that accurately describes a system where the vector is a phage.
• Eliminate other options by considering their specific hosts: Yeast expression uses yeast, and mammalian expression uses mammalian cells. Bacterial expression typically refers to using plasmids, not phages, as vectors.

Concept Tested & Keywords

• Concept Tested: Recombinant DNA Technology and Vector Types
• Stem keywords: M13 bacteriophage, vector, gene sequences, expression system
• Lead-in keywords: represents which type

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