Biotechnology had its initial impact on the pharmaceutical industry well before the perceived time. The use of fermentation technology to produce antibiotics was a cornerstone for the development of the industry. This event was both before cloning (BC) and before DNA (rather than after DNA – AD). Even now the antibiotic market, which is worth over 10 billion U.S. dollars a year, is the most valuable segment of the total market, (c.200 billion dollars per year). Nevertheless the impact of biotechnology in drug discovery was until recently perceived solely to be the use of recombinant DNA techniques to produce therapeutic proteins and modified versions of them by protein engineering.

There are several other places where genetic engineering is influencing drug discovery. The expression of recombinant proteins in surrogate systems (e.g. in E. coli, yeast or via baculovirus infection or in mammalian cells) provides materials for structure determination (e.g. HIV protease) and structure/function studies (e.g. various receptors). Recombinant DNA techniques are influencing assay technology by allowing access to proteins in sufficient quantity for high throughput screening.

In addition, screening organisms can be constructed where a particular protein function can be measured in a microorganism by complementation or via reporter gene expression.

Transgenic animals also illustrate the power of the technology for drug discovery. Not only will transgenic rats and mice be used as models of disease but also for efficacy and toxicological profiling. What is learned in transgenic rodents may well set the scene for somatic cell gene therapy in humans.