Increased dNTP levels lead to repression of the nrdAB promoter in the wild-type DHB4 and dnaNG157C strains but not in the dnaAA345S and dnaAT174P mutant strains. (A) β-Galactosidase activity, expressed in Miller units, of the nrdA'–‘lacZ fusion of a wild-type strain (DHB4), dnaAA345S, dnaAT174P and dnaNG157C strains containing an empty vector (gray) or a plasmid carrying the nrdAB operon under IPTG control, grown in presence of 100 μM IPTG to mid exponential growth. (B) β-Galactosidase activity, expressed in Miller units, of the nrdA'–‘lacZ fusion of a wild-type strain (DHB4) containing an empty vector (Ctrl) or a plasmid carrying either nrdAB, nrdHIEF, nrdEF or nrdDG under IPTG control grown in the presence of 100 μM IPTG to mid exponential growth.