Q.13

Bacterial cloning vectors and bacterial expression vectors are differentiated by the

presence of

(A) antibiotic resistance gene cassette

(B) origin of replication

(C) promoter and ribosome-binding site

(D) unique restriction sites

Bacterial cloning vectors and expression vectors differ primarily in their ability to produce proteins from inserted DNA. The correct answer to the multiple-choice question is (C) promoter and ribosome-binding site.

Correct Answer

Bacterial cloning vectors amplify foreign DNA inserts but do not drive protein production, while bacterial expression vectors enable transcription and translation into functional proteins. This distinction arises from the presence of a promoter (for RNA polymerase binding) and ribosome-binding site (RBS, like Shine-Dalgarno sequence in bacteria) in expression vectors.

Option Breakdown

• (A) Antibiotic resistance gene cassette: Both vector types include this for selecting transformed bacterial cells, such as ampicillin resistance in pBR322. It enables host survival on selective media but does not differentiate them.

• (B) Origin of replication: Essential in both for autonomous DNA replication in bacteria like E. coli, allowing multiple copies (high copy number plasmids). Shared feature, not unique to one type.

• (C) Promoter and ribosome-binding site: Correct. Cloning vectors lack these regulatory elements; expression vectors (e.g., pET series) include strong promoters (T7, lac) and RBS for gene expression, producing recombinant proteins.

• (D) Unique restriction sites: Both have multiple cloning sites (polylinkers) for inserting DNA via restriction enzymes. Common in plasmids like pUC19, not differentiating.

Practical Applications

Cloning vectors like pBR322 suit gene libraries and propagation; expression vectors like pET28a produce proteins for research or industry. Understanding this aids molecular biology workflows, from PCR cloning to purification.