PubMed · 8841750
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M Eubanks. 1996. Centered on molecules.. https://doi.org/10.1289/ehp.96104690
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Bacteria encounter acid stress under a variety of circumstances. Acid stress induces DNA damage and genomic instability, most directly via acid-catalyzed depurination reactions that generate apurinic (abasic, AP) sites on the deoxyribose phosphate backbone. DNA damage responses are important in bacterial resistance to acids. A recent report provided evidence that a DNA repair glycosylase, AlkX, which is capable of initiating the repair of interstrand DNA cross-links (ICLs), contributes to acid resistance by the pulmonary pathogen Acinetobacter baumannii (Kunkle et al. Proc. Nat. Acad. Sci. USA, 2024, 121, e2402422121). This suggested the possibility that AP-derived ICLs might contribute to the acid stress in bacteria. This idea is predicated on earlier work showing that AP sites can generate ICLs via reactions of the ring-opened AP aldehyde with the exocyclic amino groups of nucleobases on the opposing strand of duplex DNA (Price, N. E. J. Am. Chem. Soc. 2014, 136, 3483). However, it was not clear from previous work whether AP-derived ICLs could be generated under conditions of acid stress. The results reported here provide evidence for ICL formation under conditions of acid stress via a sequential process involving acid-catalyzed depurination followed by cross-linking of the resulting AP site with an adenine residue on the opposing strand of duplex DNA. This supports the possibility that AP-derived interstrand cross-links could contribute to the effects of acid stress in bacteria, and proteins involved in the repair of these lesions could be involved in resistance to acid stress.
When gene conversion is initiated by a double-strand break (DSB), any nonhomologous DNA that may be present at the ends must be removed before new DNA synthesis can be initiated. In Saccharomyces cerevisiae, removal of nonhomologous ends depends not only on the nucleotide excision repair endonuclease Rad1/Rad10 but also on Msh2 and Msh3, two proteins that are required to correct mismatched bp. These proteins have no effect when DSB ends are homologous to the donor, either in the kinetics of recombination or in the proportion of gene conversions associated with crossing-over. A second DSB repair pathway, single-strand annealing also requires Rad1/Rad10 and Msh2/Msh3, but reveals a difference in their roles. When the flanking homologous regions that anneal are 205 bp, the requirement for Msh2/Msh3 is as great as for Rad1/Rad10; but when the annealing partners are 1,170 bp, Msh2/Msh3 have little effect, while Rad1/Rad10 are still required. Mismatch repair proteins Msh6, Pms1, and Mlh1 are not required. We suggest Msh2 and Msh3 recognize not only heteroduplex loops and mismatched bp, but also branched DNA structures with a free 3' tail.
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