Fusion events between OPRTase and ODCase, which have led to the formation of the bifunctional enzyme UMPS, have occurred distinctly in different branches of the tree of life. For one thing, even though OPRTase is found at the "N"-terminus and ODCase at the "C"-terminus in most eukaryotes (e.g., Metazoa, Amoebozoa, Plantae, and Heterolobosea), the inverted fusion, which is to say OPRTase at the "C"-terminus and ODCase at the N-terminus, has also been shown to exist (e.g., parasitic protists, trypanosomastids, and stramenopiles). Moreover, other eukaryotic groups, such as Fungi, conserve both enzymes as separate proteins.