Search for Proteins Required for Accurate Gene Expression under Oxidative Stress

In aerobically growing cells, in which reactive oxygen species are produced, the guanine base is oxidized to 8-oxo-7,8-dihydroguanine, which can pair with adenine as well as cytosine. This mispairing causes alterations in gene expression, and cells possess mechanisms to prevent such outcomes. In Escherichia coli, 8-oxo-7,8-dihydroguanine-related phenotypic suppression of lacZ amber is enhanced by mutations in genes related to the prevention of abnormal protein synthesis under oxidative stress. A genome-wide search for the genes responsible, followed by DNA sequence determination, revealed that specific amino acid changes in guanylate kinase and in the β and β′ subunits of RNA polymerase cause elevated levels of phenotypic suppression, specifically under aerobic conditions. The involvement of the DnaB, DnaN, and MsbA proteins, which are involved in DNA replication and in preserving the membrane structure, was also noted. Interactions of these proteins with each other and also with other molecules may be important for preventing errors in gene expression. Background: Oxygen radicals, formed in aerobically growing cells, oxidize guanine to 8-oxo-7,8-dihydroguanine, which causes base mispairing. Results: Guanylate kinase and RNA polymerase are most responsible for preventing transcriptional errors caused by oxidative stress. Conclusion: Mutations in the genes responsible for preventing phenotypic suppression were identified. Significance: This study reveals a mechanism by which bacterial cells protect themselves against oxidative damage to RNA.