The ADE6 gene of Saccharomyces cerevisiae yeast encoding the enzyme formylglycinamidine-ribonucleotide (FGAM)-synthetase of de novo synthesis of purine nucleotides was cloned and sequenced. The gene encodes a protein consisting of 1358 amino acids. The flanking regions of 1208 (5') and 728 bp (3') were also sequenced. The nucleotide motif TGACTC inherent to the promotor regions of other purine genes of yeast was located (-276 bp) in the 5'-region of the gene. The amino acid sequence of the yeast FGAM-synthetase was found to contain repeats (Leu430-Ala620 and Pro810-Ile1000). Repeats of similar patterns of conserved amino acids were also detected in the structure of all other FGAM-synthetases. A homology of FGAM-synthetases with certain proteins of viruses from the Herpesviridae family was found.