Gene cloning involves the production in vitro of new DNA molecules which contain novel combinations of genes or oligonucleotides and the propagation of such recombinant DNA molecules by the exploitation in vivo of the replicative mechanisms of bacteria (Section 18.3) and other organisms. The developments of genetic engineering techniques have permitted the alteration of the genome of microorganisms so that it produces substances of little intrinsic value but of great medical or economic value to mankind.Foreign genes have been implanted into the DNA of E. coli to enable the production of useful proteins. Members of the antiviral family of proteins called interferons have been produced by these methods, and clinical trials to ascertain their efficacy in the treatment of certain cancers have been conducted. Human hormones such as insulin, somatostatin and somatotropin have been synthesized in E. coli. Insulin controls the level of glucose in the blood and its deficiency may result in a variety of serious diabetic conditions.