Escherichia coli response to replication stress mediated by hydroxyurea
Abstract
Error prone Y-family DNA polymerases in Escherichia coli, DNA polymerases IV and V, play a significant role in the cell's defense against exogenous and endogenous DNA damage. These polymerases are important for bypassing specific lesions present on the template DNA. We have shown (Godoy et al., 2006) that only E. coli cells expressing a carboxy-terminal truncated derivative of the catalytic subunit of DNA polymerase V, UmuC122, are resistant to the chemotherapeutic agent Hydroxyurea (HU). while umuC+ cells are highly HUS. Remarkably, umuC122::Tn5 cultures have a 100 fold elevated mutagenesis. HU inactivates class I ribonucleotide reductases (RNRs), enzymes responsible for the limiting step in deoxyribonucleotide (dNTP) formation in the cell. Therefore, HU treatment results in a dramatic reduction of intracellular concentrations of dNTPs. This dNTP limitation results in replicative DNA polymerase stalling (or replication stress) of both leading and lagging strand replication due to substrate depletion. We have also demonstrated that other gene products are part of the HUR pathway. These are dinB+, encoding DNA Pol IV, and umuD, encoding an accessory subunit of DNA Pol V. However their specific roles in this process are unknown.
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