A cDNA clone for rat liver uricase (EC 1.7.3.3), which is localized in the core of peroxisomes, was isolated from a rat liver cDNA library in lambda gt11. The clone, referred to as lambda rURC-1, induced formation of a fusion protein (molecular mass 140 kDa) in the presence of isopropyl beta-D-thiogalactoside. Immunoglobulin G reactive with the fusion protein recognized only a protein with molecular mass of 33 kDa, corresponding to the molecular mass of uricase. The nucleotide sequence of the isolated cDNA was determined and the amino acid sequence was predicted. An open reading frame was identified and found to encode a polypeptide of 280 amino acids with a molecular mass of 32226 Da. The cDNA contained 14 base pairs of 5'-untranslated sequence and 192 base pairs of 3'-untranslated sequence. The sequences of four internal peptide fragments, determined by Edman degradation, were identical to parts of the sequence predicted from the cDNA. The complete amino acid sequence predicted for rat liver uricase was compared with that of soybean nodulin uricase and nine highly homologous regions of the two enzymes were found.