Escherichia coli mutants deficient in guanine-xanthine phosphoribosyltransferase

Abstract
The purine phosphoribosyltransferases (PRTases) of E. coli were studied, and a mutant, defective in its ability to convert guanine and xanthine to their respective ribonucleotides, was isolated. The affected gene (gpt) lies between metD and proA and is 78.6% cotransducible with proA. This point mutant and a strain with a pro-lac deletion contain less than 2% of wild-type xanthine PRTase activity, yet still contain about 30% of wild-type guanine PRTase activity. The gpt gene is only 1 of at least 2 genes responsible for guanine PRTase activity in E. coli.