Gene cloning vector are small plasmid, phage or animal virus DNA molecules used to transfer a DNA fragment from a test tube into a living cell. Cloning vectors are used for obtaining millions of copies of cloned DNA fragment. The cloned genes in these vectors are not expected to express themselves at transcription or translation level.
Cloning vectors (Cloning vehicles) are used for creating genomic library or preparing probes or genetic engineering or other basic studies.
The most important requirement for recombinant DNA technology is the cloning and expression vectors The recombinant DNA is produced by cloning a foreign DNA isolated either from the genome or synthesized chemically or as cDNA using mRNA molecule. The cloning of this DNA can be done only when another DNA molecule is available that may replicate in the transformed host cell. The other DNA molecule used for joining the foreign DNA is celled Vectors.
Vecors may be plasmids, cosmids, phagemids, transposons, a virus, YAC or BAC.
Following are the desirable features for a cloning vector:
- Small size.
- Should contain origin of replication.
- Should have unique restriction sites as polylinkers or multiple cloning site (mcs).
- Should have one or more marker genes for identification ad isolation of subpopulation of bacteria containing vector.
- Should have relaxed mode of replication.
- The vector must be able to replicate in host cells.
- First artificial cloning vector (1977) constructed by Boliver & Rodriguez fromE.coli plasmid.
- It is 4362 kb long widely used cloning vector.
- pBR 322 plasmid that has been engineered in the laboratory from natural plasmids. So that it features which are useful for molecular cloning experiment.
Different Types of Vectors
|No||Cloning Vector||Insert Size (kb)|
|2||Bacteriophage||9- 22 kb|
|3||Cosmids||33- 47 kb|
|5||YAC||100 1000 kb|
BAC (Bacterial Artificial Chromosome) : A vector used to clone DNA fragments of 100-300 kb insert size in E.coli cells. Based on the naturally occurring f factor plasmid found in the bacterium E.coli.
YAC (Yeast Artificial Chromosome) : A vector of hundreds to kilobases long used for cloning of DNA fragment.
- Cosmids are the novel cloning vectors which possess properties of both plasmid and phage.
- First developed in 1978 by Barbara & John Collins.
- Cosmid can be defined as the hybrid vectors derived from plasmids which contain cos site of phage which is essential for packaging of nucleic acid into protein coat plus essential features of plasmids and several unique restriction site for the insertion of DNA to be cloned.