Sommer S, Boudsocq F, Devoret R, Bailone A
Institut Curie, Centre Universitaire, Orsay, France.
Mol Microbiol. 1998 Apr;28(2):281-91. doi: 10.1046/j.1365-2958.1998.00803.x.
The UmuD'C mutagenesis complex accumulates slowly and parsimoniously after a 12 Jm(-2) UV flash to attain after 45 min a low cell concentration between 15 and 60 complexes. Meanwhile, RecA monomers go up to 72,000 monomers. By contrast, when the UmuD'C complex is constitutively produced at a high concentration, it inhibits recombinational repair and then markedly reduces bacterial survival from DNA damage. We have isolated novel recA mutations that enable RecA to resist UmuD'C recombination inhibition. The mutations, named recA [UmuR], are located on the RecA three-dimensional structure at three sites: (i) the RecA monomer tail domain (four amino acid changes); (ii) the RecA monomer head domain (one amino acid change, which appears to interface with the amino acids in the tail domain); and (iii) in the core of a RecA monomer (one amino acid change). RecA [UmuR] proteins make recombination more efficient in the presence of UmuD'C while SOS mutagenesis is inhibited. The UmuR amino acid changes are located at a head-tail joint between RecA monomers and some are free to possibly interact with UmuD'C at the tip of a RecA polymer. These two RecA structures may constitute possible sites to which the UmuD'C complex might bind, hampering homologous recombination and favouring SOS mutagenesis.
在12 Jm(-2) 的紫外线照射后，UmuD'C诱变复合物缓慢且少量地积累，45分钟后达到15至60个复合物之间的低细胞浓度。与此同时，RecA单体增加到72,000个单体。相比之下，当UmuD'C复合物以高浓度组成性产生时，它会抑制重组修复，然后显著降低细菌因DNA损伤而存活的几率。我们分离出了新的recA突变，使RecA能够抵抗UmuD'C重组抑制。这些突变名为recA [UmuR]，位于RecA三维结构的三个位点：(i) RecA单体尾部结构域（四个氨基酸变化）；(ii) RecA单体头部结构域（一个氨基酸变化，似乎与尾部结构域中的氨基酸相互作用）；以及(iii) RecA单体的核心（一个氨基酸变化）。在UmuD'C存在的情况下，RecA [UmuR]蛋白使重组更有效，同时SOS诱变受到抑制。UmuR氨基酸变化位于RecA单体之间的头尾连接处，有些可能在RecA聚合物末端与UmuD'C自由相互作用。这两种RecA结构可能构成UmuD'C复合物可能结合的位点，从而阻碍同源重组并有利于SOS诱变。
