Common Features
Most commercial cloning vectors have key features that have made their use in molecular biology so widespread.
In the case of expression vectors, the main purpose of these vehicles is the controlled expression of a particular gene inside a convenient host organism (e.g. E. coli). Control of expression can be very important; it is usually desirable to insert the target DNA into a site that is under the control of a particular promoter. Some commonly used promoters are T7 promoters, lac promoters (bla promoter) and cauliflower mosaic virus's 35s promoter (for plant vectors).
To allow for convenient and favorable insertions, most cloning vectors have had nearly all their restriction sites engineered out of them and a synthetic multiple cloning site (MCS) inserted that contains many restriction sites. MCSs allow for insertions of DNA into the vector to be targeted and possibly directed in a chosen orientation. A selectable marker, such as an antibiotic resistance is often carried by the vector to allow the selection of positively transformed cells (see Screening below). All plasmids must carry a functional origin of replication (ORI; not shown in figure).
Some other possible features present in cloning vectors are: vir genes for plant transformation, integrase sites for chromosomal insertion, lacZα fragment for α complementation and blue-white selection, and/or reporter genes in frame with and flanking the MCS to facilitate the production of recombinant proteins .
Read more about this topic: Cloning Vector
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