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.
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.
So if there is a gene of interest for which one wants to produce a recombinant protein, how are the two types of vectors related or used? Does one first identify the gene, insert it into a cloning vector, amplify it and then transfer it into a prokaryotic cell for expressing the protein? Explanation of the steps generally followed to achieve this would be appreciated.
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