The protein and repressor nature of two regulatory gene products inE. coli has been demonstrated, employing mutants with either amber or thermosensitive mutations. The regulatory genes are thecytR and thedeoR 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 acytR or adeo R 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 acytR mutant, and much more pronounced than the glucose effect in adeo R mutant.
A model of the promoter-operator region in thedeo operon is proposed.