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Four enzymes involved in ribonucleoside and deoxyribonucleoside catabolism (deoxyribose-5-P aldolase, thymidine phosphorylase, phosphodeoxyribomutase, and purine nucleoside phosphorylase) are coded for by four closely linked structural genes on the Salmonella chromosome. The genetic order of these genes is (deoC-deoA-deoB-deoD)-serB-thr. Studies on polarity mutants and induction patterns indicate that the deoB and deoD genes may constitute a single operon and that the deoC and deoA genes may constitute a second closely linked operon.

Phosphodeoxyribomutase, the enzyme which catalyzes the interconversion of 2-deoxyribose-1-phosphate to 2-deoxyribose-5-phosphate, has been partially purified from Salmonella typhimurium. The enzyme had an absolute requirement for manganese ion and was stimulated by glucose-1, 6-diphosphate. Phosphodeoxyribomutase was induced by deoxyribose-5-phosphate and was coordinately regulated with the enzymes thymidine phosphorylase and deoxyribose-5-phosphate aldolase, type II. Mutants deficient in these three enzymes were isolated and mapped close to the threonine locus in S. typhimurium. The three enzymes thymidine phosphorylase, deoxyribose-5-phosphate aldolase, type II, and phosphodeoxyribomutase are controlled by a series of linked genes and appear to constitute an operon.