Differential effect of hydroxyurea on a ribonucleotide reductase system.

Infection of Escherichia coli with phage T4 induces a large increase in ribonucleotide reductase activity. We show that hydroxyurea inhibits T4-induced CDP, ADP, UDP, and GDP reductase activities in vitro. Moreover, there are significant differences in the degree of inhibition of each ribonucleotide reductase activity. The reductase activities for CDP and ADP are more sensitive to hydroxyurea than those for UDP and GDP, particularly at high hydroxyurea molarities. As little as 5 x 10(-4)M hydroxyurea lowers CDP and ADP reductase activities to 25 to 30% whereas as much as 0.5 M hydroxyurea is needed to lower UDP and GDP reductase activities to 50%.