1-3.5 CloningVector :

A cloning vector is defined as a vector used for replication of a cloned DNA fragment in a host cell. These vectors are frequently engineered to contain “ori” – origin of replication sites particular to the host organism. Examples of commonly used cloning vectors are: pUC18, pUC19, pBluescript vectors etc.

Fig 1-3.5 : Cloning vector

Important features of a cloning vector used to carry DNA molecules are as follows:-

• Stability in host cell: Vectors should be stabile in host cell after introduction and should not get lost in subsequent generations. This permits replication of vectors producing large copies of gene of interest.
  
  
• Ability to control their own replication: This property enables them to multiply and exist in high copy number.
  
  
• Small size: Ideal vector should be less than or equal to 10kb. The small size is essential for easy introduction in cell by transformation, transduction and electroporation.
  
  
• Multiple cloning sites: This property permits the insertion of gene of interest and plasmid re-circularization.
  
  
• Should not be transferred by conjugation: This property of vector molecule prevents recombinant DNA to escape to natural population of bacteria.
  
  
• Selectable make gene: Vector molecules should have some detectable traits. These traits enable the transformed cells to be identified among the non-transformed ones. eg. antibiotic resistance gene.