- 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.
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.
Expression vector are designed for the expression of protein product coded by that inserted gene.
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