Cloning Vector vs Expression Vector
Vector is an important term in molecular biology. In recombinant technology, the main role of a vector is to provide a mode of transport to a useful DNA fraction to be inserted into a host cell. According to the definition, it is a DNA molecule used to carry another foreign DNA artificially into a host cell to be expressed or replicated. Most used vectors are plasmids, viral vectors, cosmids and artificial chromosomes. Cloning vector and Expression vector are two types of vectors classified based on their applications.
A cloning vector is a fraction of DNA, mainly one of any mentioned vectors, which can be used to insert a foreign DNA molecule and has the ability to be inserted into a host for cloning purpose. An ideal characteristic of a cloning vector is easy insertion and removal of the DNA fragment by restriction enzyme treatment and ligating enzyme treatment. Genetically engineered plasmids are used frequently for this course.
A cloning vector should have a multiple cloning site, a selectable marker gene and a reporter gene. The purpose of a cloning site is to provide a place for cloning to occur. A selectable marker gene helps identifying successful recombinants after cloning and a reporter gene allows screening and identifies the correct recombinant among the recombinants after cloning is performed. The cloning vector does not necessarily help express a protein which the foreign DNA encodes; its sole purpose is to carry it to the host.
Expression vector is also known as an expression construct. This vector is specifically used for expression of proteins in the host cell. Like any vector, this should also contain the main parts a multiple cloning site, a marker gene and a reporter gene. The vector introduces a new gene into the host and using the host’s protein synthesis mechanism the vector allows the gene to be expressed in the host. Its initial focus is to make stable m-RNA and thereby make proteins. One good example is commercial production of insulin where the insulin gene is introduced to a bacterial plasmid and inserted back in to a E-coli bacteria body allowing the plasmids to multiply and allowing the E-coli to grow secreting insulin out which is collected and used.
For a vector to be used as an expression vector, it should have a strong promoter region, a correct translation initiation sequence and a correct terminator codon and a sequence. Expression vectors have numerous applications in producing peptides and proteins for the pharmaceutical industry such as producing insulin, growth hormone, antibiotics, vaccines, antibodies. It is also used to produce enzymes related to food and garment industries. Expression vectors are also used to produce transgenic plants such as golden rice, insect resistant plants.
What is the difference between a Cloning Vector and an Expression Vector?
• A cloning vector is used to introduce a foreign DNA fragment into a host and does not necessarily express the gene in the host
• But, expression vectors are used to express the introduced gene by producing the relevant protein.