23. Which one of the following features is NOT required in a prokaryotic expression vector?

(A) oriC
(B) Selection marker
(C) CMV promoter
(D) Ribosome binding site

Answer: (C) CMV promoter

Prokaryotic expression vectors enable protein production in bacteria like E. coli, requiring specific elements for replication, selection, and translation. The CMV promoter is eukaryotic-specific and unnecessary for prokaryotes.

Option Analysis

oriC: This chromosomal origin of replication is absent in plasmids; prokaryotic vectors instead use high-copy origins like ColE1 or pMB1 for efficient replication in bacteria.

Selection marker: Antibiotic resistance genes (e.g., ampicillin or kanamycin) or auxotrophic markers allow identification of transformed bacterial cells.

CMV promoter: Cytomegalovirus promoter drives strong expression in mammalian cells but fails in prokaryotes, which rely on bacterial promoters like lac, tac, or T7.

Ribosome binding site (RBS): Shine-Dalgarno sequence is essential for prokaryotic ribosome recruitment to initiate translation.

Prokaryotic expression vectors are essential tools in molecular biology for producing recombinant proteins in bacteria like E. coli. Key features ensure replication, selection, and gene expression tailored to prokaryotic machinery. Understanding which components are not required helps in vector design for biotechnology applications.

Essential Components

Prokaryotic vectors must include:

• Origin of replication: High-copy plasmid origins (e.g., pUC ori) replace chromosomal oriC for autonomous replication.

• Selection marker: Genes conferring antibiotic resistance select successful transformants.

• Ribosome binding site: Shine-Dalgarno sequence positions ribosomes for translation initiation.

Why CMV Promoter is Excluded

The CMV (cytomegalovirus) promoter functions in eukaryotic cells but is ineffective in prokaryotes due to incompatible sigma factors and RNA polymerase. Bacterial promoters like T7 or lacUV5 are used instead for inducible, high-level expression.

Comparison Table