Interplay of DNA repair, homologous recombination, and DNA polymerases in resistance to the DNA damaging agent 4-nitroquinoline-1-oxide in Escherichia coli

Escherichia coli has three DNA damage-inducible DNA polymerases: DNA polymerase II (Pol II), DNA polymerase IV (Pol IV), and DNA polymerase V (Pol V). While the in vivo function of Pol V is well understood, the precise roles of Pol IV and Pol II in DNA replication and repair are not as clear. Study of these polymerases has largely focused on their participation in the recovery of failed replication forks, translesion DNA synthesis, and origin-independent DNA replication. However, their roles in other repair and recombination pathways in E. coli have not been extensively examined. This study investigated how E. coli's inducible DNA polymerases and various DNA repair and recombination pathways function together to convey resistance to 4-nitroquinoline-1-oxide (NQO), a DNA damaging agent that produces replication blocking DNA base adducts. The data suggest that full resistance to this compound depends upon an intricate interplay among the activities of the inducible DNA polymerases and recombination. The data also suggest new relationships between the different pathways that process recombination intermediates.