<P> A cloning vector is a small piece of DNA, taken from a virus, a plasmid, or the cell of a higher organism, that can be stably maintained in an organism, and into which a foreign DNA fragment can be inserted for cloning purposes . The vector therefore contains features that allow for the convenient insertion or removal of a DNA fragment to or from vector, for example by treating the vector and the foreign DNA with a restriction enzyme that cuts the DNA . DNA fragments thus generated contain either blunt ends or overhangs known as sticky ends, and vector DNA and foreign DNA with compatible ends can then be joined together by molecular ligation . After a DNA fragment has been cloned into a cloning vector, it may be further subcloned into another vector designed for more specific use . </P> <P> There are many types of cloning vectors, but the most commonly used ones are genetically engineered plasmids . Cloning is generally first performed using Escherichia coli, and cloning vectors in E. coli include plasmids, bacteriophages (such as phage λ), cosmids, and bacterial artificial chromosomes (BACs). Some DNA, however, cannot be stably maintained in E. coli, for example very large DNA fragments, and other organisms such as yeast may be used . Cloning vectors in yeast include yeast artificial chromosomes (YACs). </P>

Role of vectors in cloning a dna fragment
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