Cloning and sequencing of a human cDNA coding for a multifunctional polypeptide of the purine pathway by complementation of the ade2-101 mutant in Saccharomyces cerevisiae

A HeLa cell cDNA library on a yeast expression vector was used to complement auxotrophic markers of Saccharomyces cerevisiae. Clones complementing the ade2-101 mutation harbor a 1.5 kb poly(A)+ tailed insert with a 425 amino acid open reading frame hybridizing with two human mRNAs of 1.5 kb and 3.1 kb. Its 5′ half is homologous to Bacillus subtilis SAICAR synthetase (E.C.6.3.2.6.) and its 3′ terminal half corresponds to the catalytic subunit of Escherichia coli and B. subtilis AIR carboxylase (E.C.4.1.1.21). In agreement with these homologies, pADE2H1 clones complement both ade1 and ade2 mutants of S. cerevisiae, as was also recently reported for a 3.1 kb cDNA isolated from human hepatocytes.