Project Summary:A major problem in medicine today is the emergence and persistence of antibiotic resistant bacteria. Althoughbacteria have evolved several strategies to grow in harsh environments, many bacterial species broadly copein unfavorable conditions by regulating growth and through inducing DNA damage responses. In fact, allorganisms respond to DNA damage by enlisting DNA repair pathways and by regulating cell cycle progression.Bacterial cells are constantly exposed to a broad spectrum of DNA damage caused by intracellular sources,environmental stressors, antibiotic treatments, and disinfectants applied in hospital settings. Although DNArepair and cell cycle checkpoints have been well studied in some bacteria, far less is known about theseprocesses in Gram-positive bacteria. One major challenge is that even for the most well studied Gram-positivebacterium, Bacillus subtilis, almost half of the genes in the genome are of unknown function, representing acritical and fundamental gap in our understanding of how these bacteria mitigate stress that affects growth andproliferation. While Bacillus subtilis does not cause disease, it is closely related to a number of importanthuman pathogens, including Methicillin-resistant Staphylococcus aureus, Listeria monocytogenes and severalother pathogens that are responsible for many hospital-acquired infections, which impose significant economicburdens on our healthcare system annually. Therefore, it is important to understand how a broad group ofclinically relevant bacteria respond to DNA damage and regulate cell proliferation. The long-term goal of thisresearch is to understand the contribution of unstudied genes and novel mechanisms to DNA repair and cellcycle regulation in Gram-positive bacteria. We used large-scale genome-wide approaches to identify severaluncharacterized genes that are highly conserved among Gram-positive bacteria and critical for DNA repair andregulation of cell proliferation. Two of these gene products define a new DNA excision repair pathway whilefour other genes are critical for DNA damage checkpoint recovery, allowing cells to re-enter the cell cycle afterthe damage has been repaired. We expand these experiments to continue to identify novel interactions withregulatory partners that control initiation timing and cell proliferation. We expect these studies will result in thecomplete mechanistic characterization of proteins involved in initiation, DNA repair, and cell cycle checkpoints.All of the genes we propose to study are either essential or cause severe growth defects when impaired,underscoring their importance as possible targets for novel antimicrobial therapies.