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J Bacteriol. 1968 August; 96(2): 501-514
Copyright © 1968 American Society for Microbiology. All Rights Reserved.

Characteristics of the deo Operon: Role in Thymine Utilization and Sensitivity to Deoxyribonucleosides¹

^a Department of Biological Chemistry, The University of Michigan, Ann Arbor, Michigan 48104

ABSTRACT

Inability to grow on deoxyribonucleosides as the sole carbon source is characteristic of deo mutants of Escherichia coli. Growth of deoC mutants, which lack deoxyribose 5-phosphate aldolase, is reversibly inhibited by deoxyribonucleosides through inhibition of respiration. By contrast, deoB mutants are not sensitive to deoxyribonucleosides, and deoxyribose 5-phosphate aldolase and thymidine phosphorylase are present at normal levels but are not inducible by thymidine. Organisms with the genotype deoB^–thy^– or deoC^–thy^– are able to grow on low levels of thymine, whereas deoB⁺thy^– or deoC⁺thy^– strains require high levels of thymine for growth. The deoB and deoC mutations are transducible with and map on the counterclockwise side of the threonine marker. They are closely linked to deoA, a gene determining thymidine phosphorylase. Merodiploids heterozygous for either the deoB or deoC genes are resistant to deoxyribonucleosides and, in combination with the thy mutation, require high levels of thymine for growth. Cultures of thy⁺deoC^– mutants are inhibited by thymidine until this compound has been completely degraded and excreted as deoxyribose and thymine, whereupon growth promptly resumes at a normal rate. The inhibition of respiration in deoC strains and the induction of thymidine phosphorylase and deoxyribose 5-phosphate aldolase in the wild-type organism are considered to result from the accumulation of deoxyribose 5-phosphate.

² This work was carried out during the tenure of a Post-doctoral Fellowship from the American Cancer Society, 1964–1966.

¹ A portion of this paper was presented at the 67th Annual Meeting of the American Society for Microbiology, New York, N.Y., 30 April to 4 May 1967.

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