Takahashi N K, Kusano K, Yokochi T, Kitamura Y, Yoshikura H, Kobayashi I
Department of Bacteriology, Faculty of Medicine, University of Tokyo, Japan.
J Bacteriol. 1993 Aug;175(16):5176-85. doi: 10.1128/jb.175.16.5176-5185.1993.
We had reported that a double-strand gap (ca. 300 bp long) in a duplex DNA is repaired through gene conversion copying a homologous duplex in a recB21 recC22 sbcA23 strain of Escherichia coli, as predicted on the basis of the double-strand break repair models. We have now examined various mutants for this repair capacity. (i) The recE159 mutation abolishes the reaction in the recB21C22 sbcA23 background. This result is consistent with the hypothesis that exonuclease VIII exposes a 3'-ended single strand from a double-strand break. (ii) Two recA alleles, including a complete deletion, fail to block the repair in this recBC sbcA background. (iii) Mutations in two more SOS-inducible genes, recN and recQ, do not decrease the repair. In addition, a lexA (Ind-) mutation, which blocks SOS induction, does not block the reaction. (iv) The recJ, recF, recO, and recR gene functions are nonessential in this background. (v) The RecBCD enzyme does not abolish the gap repair. We then examined genetic backgrounds other than recBC sbcA, in which the RecE pathway is not active. We failed to detect the double-strand gap repair in a rec+, a recA1, or a recB21 C22 strain, nor did we find the gap repair activity in a recD mutant or in a recB21 C22 sbcB15 sbcC201 mutant. We also failed to detect conservative repair of a simple double-strand break, which was made by restriction cleavage of an inserted linker oligonucleotide, in these backgrounds. We conclude that the RecBCD, RecBCD-, and RecF pathways cannot promote conservative double-strand break repair as the RecE and lambda Red pathways can.
我们曾报道，正如基于双链断裂修复模型所预测的那样，在大肠杆菌的recB21 recC22 sbcA23菌株中，双链DNA中的双链缺口（约300 bp长）通过基因转换复制同源双链来修复。我们现在已经检测了各种突变体的这种修复能力。(i) recE159突变消除了recB21C22 sbcA23背景下的反应。这一结果与外切核酸酶VIII从双链断裂处暴露出3'端单链的假说一致。(ii) 两个recA等位基因，包括一个完全缺失，未能在这个recBC sbcA背景下阻断修复。(iii) 另外两个SOS诱导基因recN和recQ中的突变不会降低修复。此外，阻断SOS诱导的lexA(Ind-)突变也不会阻断该反应。(iv) recJ、recF、recO和recR基因功能在这个背景下并非必需。(v) RecBCD酶不会消除缺口修复。然后，我们检测了recBC sbcA以外的其他遗传背景，在这些背景中RecE途径不活跃。我们未能在rec+、recA1或recB21 C22菌株中检测到双链缺口修复，在recD突变体或recB21 C22 sbcB15 sbcC201突变体中也未发现缺口修复活性。我们还未能在这些背景中检测到由插入的接头寡核苷酸的限制性切割产生的简单双链断裂的保守修复。我们得出结论，RecBCD、RecBCD-和RecF途径不能像RecE和λ Red途径那样促进保守的双链断裂修复。
