Difference between expression vector and cloning 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.

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.