Abstract
The XP-D/DinG family of DNA helicases participate in a variety of ways to preserve genomic stability in all three domains of life. We investigate here the genetic role of one of these proteins,YoaA, of Escherichia coli. In E. coli,YoaA has been identified as having a role in tolerance to the nucleoside azidothymidine (AZT), a DNA replication inhibitor. It is of particular interest because of its physical interaction with a component of the DNA polymerase III holoenzyme, HolC (or χ). We have proposed that this interaction competes with HolC’s interaction with HolD (or ψ) and the rest of the replisome. In this work, we map the residues of YoaA that are required for HolC interaction to the C-terminus of the protein by yeast two-hybrid analysis. We also confirm by gene fusions that YoaA is induced as part of the SOS response to DNA damage and define an upstream “LexA box” sequence in its regulation. Induction of YoaA by AZT is biphasic throughout growth of the culture with an immediate response after treatment and a slower response that peaks in the late log phase of growth. This growth-phase dependent induction by AZT is not blocked by the lexA3 (Ind-) allele, which normally negates its self-cleavage, implying another means to induce the DNA damage response that responds to the nutritional state of the cell.
