08-20-2013, 06:48 PM
A vector is a DNA molecule that has the ability to replicate autonomously in an appropriate host and into which the DNA fragment to be cloned (called DNA insert) is integrated for cloning. Therefore, a vector must have an origin of DNA replication (denoted as Ori) that functions in the host cell. Any extra-chromosomal small genome e.g., plasmid, phage or 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 is to obtain a large number of copies of the DNA insert, the vector replication must be under relaxed control that it can generate multiple copies of itself in a single host cell.
2. A vector should ideally be less than 10 kb in size because large DNA molecules are broken during purification procedure. In addition, large vectors present difficulties during various manipulations required for gene cloning.
3. The vector should be easy to isolate and purify.
4. It should be easily introduced into the host cells, i.e., transformation of the host with the vector should be easy.
5. The vector should have suitable marker genes that allow easy detection and/or selection of the transformed host cells.
6. 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.
7. The cells transformed with such vector molecules that contain the DNA insert (recombinant DNA) should be identifiable or selectable from those transformed by the vector molecule only.
8. A vector should contain unique target sites for as many restriction enzymes as possible into which the DNA insert can be integrated without disrupting an essential function.
9. When the expression of the DNA insert is desired, the vector should contain at least suitable control elements, e.g., promoter, operator, and ribosome binding sites; several other features may also be important.
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 is to obtain a large number of copies of the DNA insert, the vector replication must be under relaxed control that it can generate multiple copies of itself in a single host cell.
2. A vector should ideally be less than 10 kb in size because large DNA molecules are broken during purification procedure. In addition, large vectors present difficulties during various manipulations required for gene cloning.
3. The vector should be easy to isolate and purify.
4. It should be easily introduced into the host cells, i.e., transformation of the host with the vector should be easy.
5. The vector should have suitable marker genes that allow easy detection and/or selection of the transformed host cells.
6. 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.
7. The cells transformed with such vector molecules that contain the DNA insert (recombinant DNA) should be identifiable or selectable from those transformed by the vector molecule only.
8. A vector should contain unique target sites for as many restriction enzymes as possible into which the DNA insert can be integrated without disrupting an essential function.
9. When the expression of the DNA insert is desired, the vector should contain at least suitable control elements, e.g., promoter, operator, and ribosome binding sites; several other features may also be important.
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