Barajas-Ornelas Rocío del Carmen, Ramírez-Guadiana Fernando H, Juárez-Godínez Rafael, Ayala-García Victor M, Robleto Eduardo A, Yasbin Ronald E, Pedraza-Reyes Mario
Department of Biology, Division of Natural and Exact Sciences, University of Guanajuato, Guanajuato, Mexico.
School of Life Sciences, University of Nevada, Las Vegas, Nevada, USA.
J Bacteriol. 2014 Aug 15;196(16):3012-22. doi: 10.1128/JB.01681-14. Epub 2014 Jun 9.
In growing cells, apurinic/apyrimidinic (AP) sites generated spontaneously or resulting from the enzymatic elimination of oxidized bases must be processed by AP endonucleases before they compromise cell integrity. Here, we investigated how AP sites and the processing of these noncoding lesions by the AP endonucleases Nfo, ExoA, and Nth contribute to the production of mutations (hisC952, metB5, and leuC427) in starved cells of the Bacillus subtilis YB955 strain. Interestingly, cells from this strain that were deficient for Nfo, ExoA, and Nth accumulated a greater amount of AP sites in the stationary phase than during exponential growth. Moreover, under growth-limiting conditions, the triple nfo exoA nth knockout strain significantly increased the amounts of adaptive his, met, and leu revertants produced by the B. subtilis YB955 parental strain. Of note, the number of stationary-phase-associated reversions in the his, met, and leu alleles produced by the nfo exoA nth strain was significantly decreased following disruption of polX. In contrast, during growth, the reversion rates in the three alleles tested were significantly increased in cells of the nfo exoA nth knockout strain deficient for polymerase X (PolX). Therefore, we postulate that adaptive mutations in B. subtilis can be generated through a novel mechanism mediated by error-prone processing of AP sites accumulated in the stationary phase by the PolX DNA polymerase.
在正在生长的细胞中，自发产生的或因酶促去除氧化碱基而产生的无嘌呤/无嘧啶（AP）位点，在损害细胞完整性之前，必须由AP核酸内切酶进行处理。在此，我们研究了AP位点以及AP核酸内切酶Nfo、ExoA和Nth对这些非编码损伤的处理如何导致枯草芽孢杆菌YB955菌株饥饿细胞中突变（hisC952、metB5和leuC427）的产生。有趣的是，该菌株中缺乏Nfo、ExoA和Nth的细胞在稳定期积累的AP位点比指数生长期更多。此外，在生长受限条件下，nfo exoA nth三基因敲除菌株显著增加了枯草芽孢杆菌YB955亲本菌株产生的适应性his、met和leu回复突变体的数量。值得注意的是，在polX被破坏后，nfo exoA nth菌株产生的his、met和leu等位基因中与稳定期相关的回复突变数量显著减少。相反，在生长过程中，在缺乏聚合酶X（PolX）的nfo exoA nth敲除菌株的细胞中，所测试的三个等位基因的回复突变率显著增加。因此，我们推测枯草芽孢杆菌中的适应性突变可能通过一种新机制产生，该机制由PolX DNA聚合酶对稳定期积累的AP位点进行易错处理介导。
