Vectors are of widespread uses in the field of molecular biology. They are used as an efficient mode of transfer of foreign gene of interest into the host organism. Vectors are employed to carry foreign segment of DNA to be expressed or replicated in the host cell. Vectors are classified into the following two types depending upon their function; cloning vectors and expression vectors.
- A cloning vector acts as a vehicle to transfer the gene of interest into the host organism.
- It has an inherent ability to incorporate into the host cell.
- An essential characteristic of a cloning vector is easy insertion and removal of unwanted DNA segment by treatment with the restriction enzymes.
- A cloning vector consists of an origin of replication, a selectable marker, a reporter gene, and restriction sites.
- The origin of replication enables the cloning vector to replicate inside the host cell; utilizing the machinery of the host, and hence, obtaining multiple copies or clones.
- A selectable marker is an antibiotic resistance gene. This allows the screening of the host cells which carry the recombinant DNA from the host cells which do not carry the recombinant DNA.
- The presence of unique restriction sites aids in excision of particular sequences and hence, insertion of the desired DNA sequence.
- A reporter gene helps in identification of the successful clones and thus, their screening.
- An expression vector is also known as an expression construct.
- It is used for the expression of a protein in the host cell.
- An expression vector contains all the regulatory sequences, like promoter, ribosomal binding site, transcription initiation site, translation initiation site, that are essential for expression of the protein product.
- All these regulatory sequences utilize the machinery of the host organism.
- In addition to all these regulatory sequences, the expression vectors also contain all the elements of a typical cloning vector.
- Expression vectors have a number of uses. They are used extensively in the pharmaceutical industry for the production of peptides and proteins like insulin, antibiotics, growth factors etc.
- They are also employed to produce genetically modified organisms and transgenic plants, for example, golden rice, insect resistant plant varieties, etc.