Multiple regulation of nucleoside catabolizing enzymes: regulation of the deo operon by the cytR and deoR gene products.

The protein and repressor nature of two regulatory gene products in E. coli has been demonstrated, employing mutants with either amber or thermosensitive mutations. The regulatory genes are the cytR and the deoR genes, both of which contribute to the regulation of the synthesis of nucleoside catabolizing enzymes. Enzyme levels in strains with concurrent mutations in both regulatory genes are considerably higher than the sum of the levels in strains with a cytR or a deoR mutation alone, indicating a certain co-operativity between the two repressor proteins. The glucose repression of enzyme levels observed in the double regulatory mutant is similar to that found in a cytR mutant, and much more pronounced than the glucose effect in a deoR mutant. A model of the promoter-operator region in the deo operon is proposed.