Short-Patch Double Illegitimate Recombination (SPDIR) has been recently identified as a rare mutation mechanism. During SPDIR, ectopic DNA single-strands anneal with genomic DNA at microhomologies and get integrated during DNA replication, presumably acting as primers for Okazaki fragments. The resulting microindel mutations are highly variable in size and sequence. In the soil bacterium Acinetobacter baylyi, SPDIR is tightly controlled by genome maintenance functions including RecA. It is thought that RecA scavenges DNA single-strands and renders them unable to anneal. To further elucidate the role of RecA in this process, we investigate the roles of the upstream functions DprA, RecFOR, and RecBCD, all of which load DNA single-strands with RecA. Here we show that all three functions suppress SPDIR mutations in the wildtype to levels below the detection limit. While SPDIR mutations are slightly elevated in the absence of DprA, they are strongly increased in the absence of both DprA and RecA. This SPDIR-avoiding function of DprA is not related to its role in natural transformation. These results suggest a function for DprA in combination with RecA to avoid potentially harmful microindel mutations, and offer an explanation for the ubiquity of dprA in the genomes of naturally non-transformable bacteria.

中文翻译：

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重组起始功能 DprA 和 RecFOR 抑制贝氏不动杆菌 ADP1 中的 microindel 突变


短补丁双非法重组（SPDIR）最近被确定为一种罕见的突变机制。在 SPDIR 过程中，异位 DNA 单链与基因组 DNA 以微同源性退火，并在 DNA 复制过程中整合，可能充当冈崎片段的引物。由此产生的微插入突变在大小和序列上变化很大。在土壤细菌 Acinetobacter baylyi 中，SPDIR 受到包括 RecA 在内的基因组维护功能的严格控制。人们认为 RecA 会清除 DNA 单链并使其无法退火。为了进一步阐明 RecA 在此过程中的作用，我们研究了上游函数 DprA、RecFOR 和 RecBCD 的作用，所有这些函数都用 RecA 加载 DNA 单链。在这里，我们表明所有三个功能都将野生型中的 SPDIR 突变抑制到检测限以下的水平。虽然在 DprA 缺失的情况下 SPDIR 突变略有升高，但在 DprA 和 RecA 缺失的情况下，SPDIR 突变显着升高。 DprA 的这种避免 SPDIR 的功能与其在自然转化中的作用无关。这些结果表明 DprA 与 RecA 结合具有避免潜在有害的微插入突变的功能，并为 dprA 在天然不可转化细菌基因组中的普遍存在提供了解释。