The accumulation of glycinamide ribotide by ade3 and ade8 mutants of Saccharomyces cerevisiae

The purine intermediate GAR is present in cell free extracts of $\text{ade3}$ and $\text{ade8}$ mutants of yeast. It is also detectable following acid hydrolysis of extracts of $\text{ade6}$ and $\text{ade7}$ which accumulate FGAR and FGAM respectively. GAR accumulation is repressed by growing cells in high levels of adenine. Neither $\text{ade4}$ nor $\text{ade5}$ accumulate GAR and both prevent accumulation of GAR in $\text{ade3}$ and $\text{ade8}$ and FGAR in $\text{ade6}$. Since $\text{ade3}$ is known to be defective in folate metabolism these results indicate that $\text{ade8}$ is blocked in the conversion of GAR→FGAR.