Introduction – A historical overview
The history of rDNA technology dates back to 1865 when Gregor Mendel, using the pea plant demonstrated and proved some of the basic laws of genetics such as 1) Law of segregation, 2) Law of independent assortment and 3) Law of dominance. Mendel laid the foundation for genetics upon which experiments were conducted in later years. Later in 1915, T.H. Morgan established the fact that chromosome contains genes and these genes are linked through inheritance using Drosophila as a model organism. In 1928, Frederick Griffith observed the transformation of “rough” colonies of Streptococcus pnuemoniae into “smooth” colonies, which resulted in the fact at that time that, some information is passed on to the non-virulent strain to make it virulent. The famous “One gene - one enzyme” hypothesis was put forth by Beadle and Tatum in 1941. In 1944, Avery, MacLeod and McCarty purified DNA and proved them to be the carriers of genetic information, until which protein was believed to be the carrier.
Even before the structure was elucidated, in 1947, Erwin Chargoff postulated certain rules that DNA follows. Hershey and Chase conducted a series of experiments in 1952 to prove that DNA is the genetic material. DNA was crystallized and its helical nature was found out using X-ray crystallography by Franklin and Wilkins in 1953 and it was in the same year the 3-D structure of DNA was solved out by James Watson and Francis Crick. The later proposed the “Central Dogma of life”, where DNA produces mRNA and protein is synthesized from the mRNA through transcription and translation respectively. While Watson and Crick hinted at semi-conservative model of DNA replication, it was Meselson and Stahl in 1958 proved that replication is semi-conservative.
Molecular scissors also known as endo-nucleases, which cleaves the DNA was discovered in 1970 by Smith and Nathans. It was another milestone in rDNA technology which vastly uses these enzymes for cloning. Paul Berg in 1972 produced the first recombinant DNA using EcoRI (restriction endo-nuclease). Transformation is a technique in which DNA is incorporated into the host cell, which was first done by Boyer, Cohen and Chang in 1973. Genentech Inc. produced the first human protein somatostatin from a transgenic bacterium in 1977, which is considered as the advent of the age of biotechnology. Since then several techniques has been improved and several therapeutically important proteins were produced by using rDNA technology.
The first step in generating a recombinant DNA is to identify and isolate the gene of interest. Then the isolated DNA fragment is incorporated into a suitable vector. The vector containing the gene of interest is transformed into the host cell, where it replicates independently and produces copies as the host cell multiplies. Positive clones are selected and harvested. The gene incorporated in the vector is controlled by a genetic switch which regulates the...