Properties of Good Vector,Objective of Cloning,Vector Replication,Genome,Ribosome Binding Sites,DNA Molecules

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	Properties of Good Vector - 1. It should be able to replicate autonomously. When the objective of cloning is to obtain a large number of copies of the DNA insert, the vector replication must be under relaxed control so that it can generate multiple copies of itself in a single host cell.S 2. It should be easy to isolate and purify. 3. It should be easily introduced into the host cells, Le., transformation of the host with the vector should be easy.
4. The vector should have suitable marker genes that allow easy detection and/or selection of the transformed host cells. 5. When the objective is gene transfer, it should have the ability to integrate either itself or the DNA insert it carries into the genome of the host cell.
6. The cells transformed with the vector containing the DNA insert (recombinant DNA) should be identifiable be selectable from those transformed by the unaltered vector. 7. A vector should contain unique target sites for as may restriction enzymes as possible into which the DNA insert can be integrated. 8. When expression of the DNA insert is desired, the vector should contain atleast suitable control elements, e.g., promoter, operator and ribosome binding sites. 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 of gene is to be cloned. In addition, (2) most naturally occurring vectors do not have all the required functions; therefore, useful vectors have been created by joining together segments performing specific functions (called modules) from two or more natural entities.