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DNA replication is essential for cells to grow and divide. Ribonucleotide reductase is an essential enzyme that is responsible for the formation of deoxyribonucleotides that are used in DNA synthesis during replication . Hydroxyurea is a chemotherapeutic agent that is thought to work by specifically inhibiting the ribonuceotide reductase to prevent replication. However, recent studies in E. coli have shown that following an initial period of inhibition, DNA synthesis then recovers in the presence of hydroxyurea, suggesting that the mode of death and cellular response to hydroxyurea is more complex than originally proposed. The E.coli genome encodes three ribonucleotide reductases that are thought to operate under distinct cellular conditions. Here, we examined whether either of the two alternative riboucleotide reductases may be resistant to hydroxyurea treatment and allow replication to recover in its presence. To test this, mutants lacking either the iron-starvation reductase, NrdEF, or the anaerobic reductase, NrdDG were examined for their ability to recover DNA synthesis in the presence of hydroxyurea. We observed that, both nrdEF and nrdDG mutants recovered replication similar to wild type cultures, suggesting that these enzymes are not responsible for the observed recovery. We discuss these results in relation to their implications for the mechanism by which hydroxyurea operates to inhibit and kill growing cells.

psu mcnair scholars online journal

Characterization of the Role that Alternative Ribonucleotide Reductases Play in Restoring Replication in the Presence of Hydroxyurea in Escherichia Coli