In general, cloning vectors are plasmids that are used primarily to propagate DNA. They replicate in E. coli to high copy numbers and contain a multiple cloning site (also called a polylinker) with restriction sites used for inserting a DNA fragment.
A cloning vector is a small piece of DNA that can be stably maintained in an organism, and into which a foreign DNA fragment can be inserted for cloning purposes. The cloning vector may be DNA taken from a virus, the cell of a higher organism, or it may be the plasmid of a bacterium.
Characteristics of a cloning vectors
it must be small in size. It must be self-replicating inside host cell. It must possess restriction site for Restriction Endonuclease enzymes. Introduction of donor DNA fragment must not interfere with replication property of the vector.