To become a successful plasmid cloning vector, it must be a small DNA molecule that can be self-replicating inside host cells, which generally has several essential features as follows:

• Origin of replication: It is the site where replication is initiated.
• Marker genes for selection and/or screening: These genes allow to screen out cells that lack specific genes, e.g. antibiotic resistance genes, and also are used to test difference in phenotype between cells.
• Unique and multiple restriction sites: The restriction sites for various restriction endonucleases allow insertion of foreign DNA to specific sites on plasmid.
• Promoters for gene expression: It is an essential component of expression vectors, which drives the transcription of the vector’s transgene and helps in getting the cloned product expressed.