SACCHAROMYCES-CEREVISIAE EXPRESSES 2 GENES ENCODING ISOZYMES OF 5-AMINOIMIDAZOLE-4-CARBOXAMIDE RIBONUCLEOTIDE TRANSFORMYLASE

We have isolated and cloned two Saccharomyces cerevisiae genes which e ncode isozymes of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR ) transformylase, the ninth step of the de novo purine biosynthesis pa thway, This reaction involves the formylation of AICAR using 10-formyl tetrahydrofolate as the formyl donor, ADE16 is located on chromosome M I and encodes an open reading frame of 591 amino acids, ADE17 is locat ed on chromosome XIII and encodes an open reading frame of 592 amino a cids, The deduced amino acid sequences of the two genes are 84% identi cal to each other and are 60-63% identical to the chicken and human bi functional AICAR transformylase/IMP cyclohydrolase amino acid sequence s. Disruption of the two chromosomal yeast genes resulted in adenine a uxotrophy, while the expression of either gene alone was sufficient to support growth without adenine, lie vitro assays of AICAR transformyl ase activity demonstrated the lack of IMP production in the double dis ruptant strain, S. cerevisiae is the only organism known thus far to p ossess isozymes of this protein, Because it is likely that the protein s encoded by ADE16 and ADE17 also contain IMP cyclohydrolase activity, these two genes complete the set of clones and mutants for the entire de novo purine biosynthesis pathway in yeast. (C) 1997 Academic Press .