ジャーナル: Nature / 年: 2011 タイトル: Structures of the RNA-guided surveillance complex from a bacterial immune system. 著者: Blake Wiedenheft / Gabriel C Lander / Kaihong Zhou / Matthijs M Jore / Stan J J Brouns / John van der Oost / Jennifer A Doudna / Eva Nogales / 要旨: Bacteria and archaea acquire resistance to viruses and plasmids by integrating short fragments of foreign DNA into clustered regularly interspaced short palindromic repeats (CRISPRs). These ...Bacteria and archaea acquire resistance to viruses and plasmids by integrating short fragments of foreign DNA into clustered regularly interspaced short palindromic repeats (CRISPRs). These repetitive loci maintain a genetic record of all prior encounters with foreign transgressors. CRISPRs are transcribed and the long primary transcript is processed into a library of short CRISPR-derived RNAs (crRNAs) that contain a unique sequence complementary to a foreign nucleic-acid challenger. In Escherichia coli, crRNAs are incorporated into a multisubunit surveillance complex called Cascade (CRISPR-associated complex for antiviral defence), which is required for protection against bacteriophages. Here we use cryo-electron microscopy to determine the subnanometre structures of Cascade before and after binding to a target sequence. These structures reveal a sea-horse-shaped architecture in which the crRNA is displayed along a helical arrangement of protein subunits that protect the crRNA from degradation while maintaining its availability for base pairing. Cascade engages invading nucleic acids through high-affinity base-pairing interactions near the 5' end of the crRNA. Base pairing extends along the crRNA, resulting in a series of short helical segments that trigger a concerted conformational change. This conformational rearrangement may serve as a signal that recruits a trans-acting nuclease (Cas3) for destruction of invading nucleic-acid sequences.
凍結剤: ETHANE / チャンバー内湿度: 95 % / チャンバー内温度: 78 K / 装置: OTHER 詳細: Vitrification instrument: Vitrobot. blotting at 4 degrees C 手法: 4 microliter aliquot of purified sample placed onto C-flat that had been glow-discharged in a nitrogen atmosphere for 60 sec using an Edwards Carbon Evaporator. The grids were blotted for 3 ...手法: 4 microliter aliquot of purified sample placed onto C-flat that had been glow-discharged in a nitrogen atmosphere for 60 sec using an Edwards Carbon Evaporator. The grids were blotted for 3 seconds using a blotting offset of -1.