Human allantoicase gene: cDNA cloning, genomic organization and chromosome localization

Uric-acid-degrading enzymes (uricase, allantoinase, allantoicase, ureidoglycolate lyase and urease) were lost during vertebrate evolution and the causes for this loss are still unclear. We have recently cloned the first vertebrate allantoicase cDNA from the amphibian Xenopus laevis. Surprisingly, we have found some mammalian expressed sequence tags (ESTs) that show high similarity with Xenopus allantoicase cDNA. From a human fetal spleen cDNA library and adult kidney EST clone, we have obtained a 1790 nucleotide long cDNA. The 3' end of this sequence reveals a substantial high identity with the corresponding portion of Xenopus allantoicase cDNA. In contrast, at the 5' end the human sequence diverges from that of Xenopus; since no continuous open reading frame can be found in this region, the hypothetical human protein appears truncated at its N-terminus. We proposed that such a transcript could be due to an incorrect splicing mechanism that introduces an intron portion at the 5' end of human cDNA. Allantoicase cDNA is expressed in adult testis, prostate, kidney and fetal spleen. By comparison with available genomic sequences deposited in database, we have determined that the human allantoicase gene consists of five exons and spans 8kb. We have also mapped the gene in chromosome 2.