02445nam a2200325Ia 4500003001000000005001700010040000900027245008500036490003900121520147000160650001701630650001701647650001701664650001701681650001701698650001701715650002201732650000801754650002201762700001901784700001701803700001301820700001501833700001901848700002101867700001701888700001701905856015601922008004102078MX-MdCICY20260521091516.0  cCICY10aStructures of the RNA-guided surveillance complex from a bacterial immune system0 vNature, 477(7365), p.486-489, 20113 aBacteria 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 5-2 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.14aNUCLEIC ACID14aPROTEIN CASA14aPROTEIN CASB14aPROTEIN CASC14aPROTEIN CASD14aPROTEIN CASE14aRIBONUCLEOPROTEIN14aRNA14aUNCLASSIFIED DRUG12aWiedenheft, B.12aLander, G.C.12aZhou, K.12aJore, M.M.12aBrouns, S.J.J.12aVan Der Oost, J.12aDoudna, J.A.12aDoudna, J.A.40uhttps://drive.google.com/file/d/127a8PBRy3Qyv2txdjpG_7COpneyzf-uE/view?usp=drivesdkzPara ver el documento ingresa a Google con tu cuenta: @cicy.edu.mx250602s9999    xx |||||s2   |||| ||und|d