Zaychikov E, Martin E, Denissova L, Kozlov M, Markovtsov V, Kashlev M, Heumann H, Nikiforov V, Goldfarb A, Mustaev A
Limnological Institute, Russian Academy of Sciences, Irkutsk, Russia.
Science. 1996 Jul 5;273(5271):107-9. doi: 10.1126/science.273.5271.107.
When the Mg2+ ion in the catalytic center of Escherichia coli RNA polymerase (RNAP) is replaced with Fe2+, hydroxyl radicals are generated. In the promoter complex, such radicals cleave template DNA near the transcription start site, whereas the beta' subunit is cleaved at a conserved motif NADFDGD (Asn-Ala-Asp-Phe-Asp-Gly-Asp). Substitution of the three aspartate residues with alanine creates a dominant lethal mutation. The mutant RNAP is catalytically inactive but can bind promoters and form an open complex. The mutant fails to support Fe2+-induced cleavage of DNA or protein. Thus, the NAD-FDGD motif is involved in chelation of the active center Mg2+.
当大肠杆菌RNA聚合酶（RNAP）催化中心的Mg2+离子被Fe2+取代时，会产生羟基自由基。在启动子复合物中，这些自由基会在转录起始位点附近切割模板DNA，而β'亚基则在保守基序NADFDGD（天冬酰胺-丙氨酸-天冬氨酸-苯丙氨酸-天冬氨酸-甘氨酸-天冬氨酸）处被切割。将三个天冬氨酸残基替换为丙氨酸会产生显性致死突变。突变的RNAP催化无活性，但能结合启动子并形成开放复合物。该突变体无法支持Fe2+诱导的DNA或蛋白质切割。因此，NAD-FDGD基序参与活性中心Mg2+的螯合。
