RELATIONSHIP BETWEEN SITE OF GENETIC BLOCK IN THYMINE-LESS MUTANTS AND ENZYME ACTIVITIES IN DEOXYRIBONUCLEOSIDE CATABOLISM IN ESCHERICHIA COLI K12

1. Biochemical characteristics of two types of thymine-less mutant of E. coli K12 with high and low thymine requirements (Thy20- and Thy2-) were compared. 2. The excretion of deoxyribose into the medium by Thy2- during thymine starvation was a unique character associated with the mutation of Thy20- to Thy2-, suggesting a deficiency of phosphodeoxyribomutase (Mut) and/or deoxyriboaldolase (Aid) which participate in deoxyribonucleoside catabolism. 3. The mutation also results in change in the activities and inducibilities of thymidine phosphorylase (Tpp), purine nucleoside phosphorylase (Pup) and deoxyriboaldolase (Aid). Thy2- mutants were classified into four groups on the characters of these enzymes: 1) constitutive and may lack Mut, 2) inducible by thymidine or thymine starvation and lack Ald, 3a) non-inducible and may lack Mut, and 3b) non- or only slightly inducible and lack Ald, 4. Our data together with those of genetical studies show that a) the gene specifying all four enzymes participating in the catabolism of deoxyribonucleosides — Tpp, Pup, Ald, and Mut — might constitute an operon. The inducer for the operon is suggested to be dR-1-P, b) Accumulation of dR-5-P in the cells inhibits bacterial growth. © 1969, The Genetics Society of Japan. All rights reserved.