The Different host specific vectors, we are going to discuss as follows-

Bacterial Plasmid

Phage based vectors

Yeast vectors

Mammalian vectors

Bacterial Plasmid : Plasmid are widely been used for cloning of foreign DNA into the bacteria as host strain. Before getting into the details of discussing bacterial plasmid we will discuss the basic properties of plasmids.   

Different forms of plasmids: Bacterial plasmid is a double stranded circular DNA exists in 3 different forms (Figure 17.1). If both the strands of circular double strands are intact then it is called as covalently closed circles (CCC) where as if one of the strand has nick, then it acquire the conformation of open circle DNA (OC, DNA). During the isolation of plasmid DNA from bacteria, covalently closed circular DNA loses few number of turns and as a result it acquire supercoiled configuration. The interchange between these different forms are possible under the in-vitro or in-vivo conditions, such as DNA gyrase produces additional turn into the circular DNA to adopt supercoiled conformation.

Figure 17.1: Different forms of plasmids