Strains of Saccharomyces cerevisiae producing Aspergillus flavus uricase (Uox) have been constructed. An artificial promoter which combined the upstream and downstream sequences of the GAL7 and ADH2 promoters, respectively, was found to be efficient in directing the synthesis of uaZ mRNAs encoding Uox. A good proportionality between the copy number of the uaZ expression cassette and the level of Uox production was found in the range of 1-10 copies. Transformants accumulated active and soluble Uox to a level exceeding 13% of total protein, as deduced from enzymatic assays. This relative level could be improved two- to threefold by using a recipient strain in which the wild-type GAL4 gene had been deleted and which expressed a GAL4 construct placed under the control of the ADH2 promoter.