Following are the properties which make plasmids good cloning vectors:
i) Self-replicating: Plasmids contains origin of replication and hence they are able to multiply by themselves independently of the chromosomal DNA. They maintain their number in progenies.
ii) Low molecular weight: Plasmids have low molecular weight which makes them easy to handle and hence can be present in multiple copies.
iii) Multiple Cloning Sites: This is a site on plasmid which has recognition sites for many restriction enzymes.
iv) Selectable Marker: Plasmid has certain genes which help in identifying the transformed cells. For example, antibiotic resistance genes.
v) High copy number: Due to low molecular weight of plasmids, they are present in multiple copies. High copy number plasmids are require to produce large quantities of the recombinant DNA.
vi) Host range: Plasmids used as coning vectors have narrow host range so that transmission of these plasmids to other organism in environment is avoided.