Difference between Cloning Vector and Expression Vector

Cloning vectors are the DNA molecules that can carry a foreign DNA segment into the the host cell.The vectors used in recombinant DNA technology can be plasmids, cosmids, bacteriophages etc.

• Plasmids: Self replicating, circular,  extra chromosomal DNA present in bacteria. Plasmids have only one or two copies per cell.
• Bacteriophages: Virus infecting bacteria. Bacteriophages have high number per cell, so their copy number  is also high in genome.
• Cosmids: Hybrid vectors derived from plasmids which contain cos site of lambda phage.

Feature required to facilitate cloning into vector: Origin of replication, Selectable marker, unique restriction sites.
The purpose of cloning vector is often to make numerous copies of the inserted gene.

> Gene cloning vectors: Essential features > Shuttle vector vs Expression Vector

Expression Vectors: The cloning vector containing suitable expression signals to have maximum gene expression, is called expression vector.
The following expression signals are introduced into gene cloned vectors to get maximum expression:

• Insertion of a strong promoter.
• Insertion of a strong termination codon.
• Adjustment of distance between promoter and cloned gene.
• Insertion of transcription termination sequence.
• Insertion of a strong translation initiation sequence.  

Example: An expression vector pSOMI containing promoter operator (PO) for production of a chain of somatostatin (somI).
Expression vector are designed for the expression of protein product coded by that inserted gene.