ABSTRACT
One of the most important elements in recombinant DNA (rDNA) technology or in gene cloning is the vector. A random DNA or cDNA segment or specific gene is linked into a vector to form rDNA molecule, which can be propagated in suitable host cells to a large number, is a cloning vector. There are different types of cloning vectors for use with different types of host cells. The largest number exists for E. coli and the best known of these is the plasmid vector. Plasmids are double-stranded, closed circular DNA molecules, which exist in the cell as extrachromosomal units. There are three general classes of plasmids: virulence plasmids, which encode toxin genes, drug resistance plasmids, which confer resistance to antibiotics, and plasmids, which encode genes required for bacterial conjugation. A plasmid vector used for cloning is specifically developed by adding certain features. The chapter describes some of the plasmid vectors.
