Editing Recombinant DNA (section)

===Recombinant chymosin===
Found in [[rennet]], [[chymosin]] is the enzyme responsible for hydrolysis of ''κ''-[[casein]] to produce para-''κ''-casein and [[glycomacropeptide]], which is the first step in formation of [[cheese]], and subsequently [[curd]], and [[whey]].<ref>{{cite book |doi=10.1533/9780857093639.13 |chapter=Caseins |title=Handbook of Food Proteins |date=2011 |last1=O'Kennedy |first1=B.T. |pages=13–29 |isbn=978-1-84569-758-7 }}</ref> It was the first genetically engineered food additive used commercially. Traditionally, processors obtained chymosin from rennet, a preparation derived from the fourth stomach of milk-fed calves. Scientists engineered a non-pathogenic strain (K-12) of ''[[E. coli]]'' bacteria for large-scale laboratory production of the enzyme. This microbiologically produced recombinant enzyme, identical structurally to the calf derived enzyme, costs less and is produced in abundant quantities. Today about 60% of U.S. hard cheese is made with genetically engineered chymosin. In 1990, FDA granted chymosin "[[generally recognized as safe]]" (GRAS) status based on data showing that the enzyme was safe.<ref>Donna U. Vogt and Mickey Parish. (1999) [https://fpc.state.gov/6176.htm Food Biotechnology in the United States: Science, Regulation, and Issues]</ref>