Vectors

A Vector is a DNA molecule that has the ability to replicate in an appropriate hostcellm and into which the DNA fragment to be cloned called DNA insert is intergrated fro cloning. Therefore, vector must have an origin of DNA replication that functions in the host cell. ANy extra chromosomal small genome e.g plasmid phage and virus, may be used as a vector.
Properties of A good vector
A good vector must have the following properties.
1. It should be able to replicate autonomously, when the objective of cloning it to obtain a large number of copies of the DNA insert, the vector replicon must be under relaaxed control so that if can generate multiple copies of itself an a single host cell.
2. IT should be easy to isolate and purify.
3. it should be easily introduced into the host cells, transformation of the host with the vector should be easy.
4. The vector should have suitable marker genes that aloow easy detection or selection of the transformed host cell.
5. When the objective is gene transfer, it should have the ability to intergrate either itself or the DNA insert it carries into the genome of the host cell.
6. The cells transformed with the vector molecules containing the DNA insert recombinant or chimaeric vector should be identifiable or selectable from those transformed by the vector molecules only.
7. A vector should contain unique target sites for as many restriction enzymes as possible into which the DNA insert can be integrated without disruptin an essential function.
8. When expression of the DNA insert is desiredm the vector should contain atleast suitable control elements, e.g promoter operator and ribosome binding sites several other features may also be important.
It should be kept in mind that (1) the DNA molecules used as vectors have coevolved with their specific natural host species, and hence are adapted to function well in them and in their closely related species. Therefore, the choice of vector depends largely on the host species into which the DNA insert or gene is to be cloned. In addition, (2) most naturally occuring vectors do not have all the required functions therefore, useful vectors have been created by joining together segments performing specific functions from two or more natural entities.