Enables orotate phosphoribosyltransferase activity and orotidine-5'-phosphate decarboxylase activity. Involved in several processes, including determination of adult lifespan; pyrimidine-containing compound biosynthetic process; and response to radiation. Located in cytoplasm. Expressed in head; intestine; neurons; and tail. Used to study orotic aciduria. Human ortholog(s) of this gene implicated in orotic aciduria and purine-pyrimidine metabolic disorder. Is an ortholog of human UMPS (uridine monophosphate synthetase).