FIGURE 1.

The de novo and salvage pathways for purine nucleotide biosynthesis. The pathway of adenosine/inosine toxicity is highlighted. Dashdot lines indicate the reversible reactions catalyzed by purine nucleoside phosphorylase (deoD); most strains employed in this study are null for the enzyme. Dashed lines indicate feedback regulation of PRPP synthetase by ADP and AMP. The gene designations are: purA, adenylosuccinate synthetase; purB, adenylosuccinate lyase; guaB, IMP dehydrogenase; guaA, GMP synthetase; deoD, purine nucleoside phosphorylase; hpt, guanine-hypoxanthine phosphoribosyltransferase; gpt, guanine phosphoribosyltransferase; gsk, guanosine-inosine kinase; apt, adenine phosphoribosyltransferase; add, adenosine deaminase; guaC, GMP reductase; prs, PRPP synthetase.