Rehrauer W M, Lavery P E, Palmer E L, Singh R N, Kowalczykowski S C
Department of Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
J Biol Chem. 1996 Sep 27;271(39):23865-73.
Essential to the two distinct cellular events of genetic recombination and SOS induction in Escherichia coli, RecA protein promotes the homologous pairing and exchange of DNA strands and the proteolytic cleavage of the LexA repressor, respectively. Since both of these activities require single-stranded DNA (ssDNA) and ATP, the inter-relationship between these reactions was investigated and found to display many parallels. The extent of active complex formed between RecA protein and M13 ssDNA, as measured by both ATP hydrolysis and LexA proteolysis, is stimulated in a similar manner by either a reduction in magnesium ion concentration or the presence of single-stranded DNA binding (SSB) protein. However, unexpectedly, SSB protein inhibits both LexA proteolysis and ATP hydrolysis (in assays containing repressor) at concentrations of RecA protein that are substoichiometric to the ssDNA, arguing that LexA repressor affects the competition between RecA and SSB proteins for limited ssDNA binding sites. Additionally, attenuation of LexA repressor cleavage in the presence of double-stranded DNA or by an excess of ssDNA suggests that interaction of the RecA nucleoprotein filament with either LexA repressor or a secondary DNA molecule is mutually exclusive. The significance of these results is discussed in the context of both the regulation of inducible responses to DNA damage, and the competitive relationship between the processes of SOS induction and genetic recombination.
RecA蛋白对于大肠杆菌中基因重组和SOS诱导这两个不同的细胞事件至关重要，它分别促进DNA链的同源配对和交换以及LexA阻遏物的蛋白水解切割。由于这两种活性都需要单链DNA（ssDNA）和ATP，因此对这些反应之间的相互关系进行了研究，发现它们有许多相似之处。通过ATP水解和LexA蛋白水解测量，RecA蛋白与M13 ssDNA形成的活性复合物的程度，在镁离子浓度降低或存在单链DNA结合（SSB）蛋白时，以类似的方式受到刺激。然而，出乎意料的是，在RecA蛋白浓度低于与ssDNA化学计量比的情况下，SSB蛋白会抑制LexA蛋白水解和ATP水解（在含有阻遏物的测定中），这表明LexA阻遏物影响RecA和SSB蛋白对有限的ssDNA结合位点的竞争。此外，在双链DNA存在下或过量ssDNA时LexA阻遏物切割的减弱表明，RecA核蛋白细丝与LexA阻遏物或第二个DNA分子的相互作用是相互排斥的。在对DNA损伤的诱导反应的调节以及SOS诱导和基因重组过程之间的竞争关系的背景下，讨论了这些结果的意义。
