Oxidative damage to DNA is a threat to the genomic integrity and coding accuracy of the chromosomes of all living organisms. Guanine is particularly susceptible to oxidation, and 8-oxo-dG (OG), when produced in situ or incorporated by DNA polymerases, is highly mutagenic due to mispairing with adenine. In many bacteria, defense against OG depends on MutT enzymes, which sanitize OG in the nucleotide pool, and the MutM/Y system, which counteracts OG in chromosomal DNA. In Escherichia coli, antibiotic lethality has been linked to oxidative stress and the downstream consequences of OG processing. However, in mycobacteria, the role of these systems in genomic integrity and antibiotic lethality is not understood, in part because mycobacteria encode four MutT enzymes and two MutMs, suggesting substantial redundancy. Here, we definitively probe the role of OG handling systems in mycobacteria. We find that, although MutT4 is the only MutT enzyme required for resistance to oxidative stress, this effect is not due to OG processing. We find that the dominant system that defends against OG-mediated mutagenesis is MutY/MutM1, and this system is dedicated to in situ chromosomal oxidation rather than correcting OG incorporated by accessory polymerases (DinB1/DinB2/DinB3/DnaE2). In addition, we uncover that mycobacteria resist antibiotic lethality through nucleotide sanitization by MutTs, and in the absence of this system, accessory DNA polymerases and MutY/M contribute to antibiotic-induced lethality. These results reveal a complex, multitiered system of OG handling in mycobacteria with roles in oxidative stress resistance, mutagenesis, and antibiotic lethality.

对DNA的氧化损伤威胁到所有活生物体染色体的基因组完整性和编码准确性。鸟嘌呤特别容易氧化，当原位产生或通过DNA聚合酶掺入8-氧代-dG（OG）时，由于与腺嘌呤错配而高度致突变。在许多细菌中，对OG的防御取决于MutT酶和MutM / Y系统，该MutT酶可对核苷酸库中的OG进行消毒，该系统可抵消染色体DNA中的OG。在大肠杆菌中，抗生素致死率与氧化应激和OG加工的下游后果有关。但是，在分枝杆菌中，这些系统在基因组完整性和抗生素致死性方面的作用尚不清楚，部分原因是分枝杆菌编码四种MutT酶和两种MutM，这表明存在大量冗余。在这里，我们明确地探讨了OG处理系统在分枝杆菌中的作用。我们发现，尽管MutT4是抵抗氧化应激所需的唯一MutT酶，但这种作用并非归因于OG加工。我们发现防御OG介导的诱变的主要系统是MutY / MutM1，并且该系统专用于原位染色体氧化，而不是校正由辅助聚合酶（DinB1 / DinB2 / DinB3 / DnaE2）掺入的OG。此外，我们发现分枝杆菌可通过MutTs进行的核苷酸消毒来抵抗抗生素致死性，并且在没有该系统的情况下，辅助DNA聚合酶和MutY / M会导致抗生素致死性。这些结果揭示了分枝杆菌中OG处理的复杂，多层系统，在氧化应激抗性，诱变和抗生素致死性方面发挥作用。