The first three enzymes of the process are all coded by the same gene in CAD which consists of carbamoyl phosphate synthetase II, aspartate carbamoyltransferase and dihydroorotase.
UMPS is a bifunctional enzyme consisting of orotate phosphoribosyltransferase (OPRT) and orotidine monophosphate decarboxylase (OMPDC).
[8] Through negative feedback inhibition, the end-products UTP and UDP prevent the enzyme CAD from catalyzing the reaction in animals.
RNA is composed of pyrimidine and purine nucleotides, both of which are necessary for reliable information transfer, and thus natural selection and Darwinian evolution.
Becker et al. showed how pyrimidine nucleosides can be synthesized from small molecules and ribose, driven solely by wet-dry cycles.