Mutants Constitutive for Nucleoside-Catabolizing Enzymes in Escherichia coli K 12. Isolation, Characterization and Mapping

Abstract

Regulatory mutants of Escherichia coli, which synthesize cytidine deaminase and uridine phosphorylase constitutively have been isolated by different selection procedures and have been characterized. These mutants were also found to synthesize four other nucleoside-catabolizing enzymes, thymidine phosphorylase, deoxyriboaldolase, phosphodeoxyribomutase and purine nucleoside phosphorylase in amounts 3- to 10-fold in excess of wild-type levels. This phenotype was found to be caused by mutations in one regulatory gene designated cytR. Another class of regulatory mutants containing levels of deoxyriboaldolase, thymidine phosphorylase, phosphodeoxyribomutase and purine nucleoside phosphorylase 10- to 100-fold above wild-type levels have been isolated by similar selection procedures. These mutants are a result of a mutation in another regulatory gene, designated deoR, and were shown to contain low, inducible levels of cytidine deaminase and uridine phosphorylase. The cytR and deoR genes have been found by P1-mediated transductions to be located at 76.5 min and 18.5 min, respectively, on the E. coli chromosome.