Aertsen Abram, Tesfazgi Mebrhatu Mehari, Michiels Chris W
Laboratory of Food Microbiology, Centre for Food and Microbial Technology, Department of Microbial and Molecular Systems (M(2)S), Faculty of Bioscience Engineering, K.U.Leuven, Kasteelpark Arenberg 22, B-3001 Leuven, Belgium.
Biochem Biophys Res Commun. 2008 Mar 7;367(2):435-9. doi: 10.1016/j.bbrc.2007.12.151. Epub 2008 Jan 4.
The Mrr protein of Escherichia coli K12 is a cryptic type IV restriction endonuclease with specificity for methylated DNA. Recently it was discovered that endogenous activation of E. coli Mrr could be triggered by high pressure stress, resulting in the generation of double strand breaks in the host chromosome and concomitant induction of the SOS response. In this report we focused on Mrr activity of Salmonella Typhimurium LT2, and although we surprisingly found no evidence of high pressure induced activation, a large number of constitutively activated Mrr mutants could be isolated when the mrr gene was routinely cloned in an expression vector. Analysis of several spontaneous mutants revealed different single mutations that rendered the Mrr protein constitutively active. Moreover, a spontaneous S. Typhimurium mutant could be isolated that displayed an increased basal SOS induction because of a point mutation in the chromosomal mrr gene. Based on these findings the physiological role of Mrr in the cell is discussed.
大肠杆菌K12的Mrr蛋白是一种对甲基化DNA具有特异性的隐性IV型限制性内切核酸酶。最近发现，高压胁迫可触发大肠杆菌Mrr的内源性激活，导致宿主染色体中产生双链断裂并伴随SOS反应的诱导。在本报告中，我们重点研究了鼠伤寒沙门氏菌LT2的Mrr活性，尽管我们令人惊讶地未发现高压诱导激活的证据，但当mrr基因常规克隆到表达载体中时，可以分离出大量组成型激活的Mrr突变体。对几个自发突变体的分析揭示了使Mrr蛋白组成型激活的不同单突变。此外，由于染色体mrr基因中的点突变，可以分离出一个显示基础SOS诱导增加的自发鼠伤寒沙门氏菌突变体。基于这些发现，讨论了Mrr在细胞中的生理作用。
