The cDNA of human amidophosphoribosyltransferase (EC 2.4.2.14, ATase), which is the supposed regulatory allosteric enzyme of de novo purine nucleotide biosynthesis, has been cloned from human hepatoma (HepG2) cDNA library. The predicted open reading frame encodes a protein of 517 amino acids with a deduced molecular weight (Mr) of 57,398, which is consistent with the molecular mass of 56 kDa on SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of the ATase subunit purified from human placenta. The derived amino acid sequence exhibits 93, 82, 41, 37, and 33% identity with the sequences of rat, chicken, Bacillus subtilis, Escherichia coli, and Saccharomyces cerevisiae ATases, respectively. Southern blot analysis suggested that the ATase gene exists as multiple copies. ATase mRNA (3.5 kb) is ubiquitously expressed in various human tissues. Comparison with rat and chicken ATases showed that two cysteine residues for an iron-sulfur cluster were conserved. Four consensus phosphorylation sites for cAMP-dependent protein kinase were found.