02524nam a2200361Ia 4500 MX-MdCICY 20260521091516.0 CICY B-16136 Structures of the RNA-guided surveillance complex from a bacterial immune system Nature, 477(7365), p.486-489, 2011 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 5-2 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. NUCLEIC ACID PROTEIN CASA PROTEIN CASB PROTEIN CASC PROTEIN CASD PROTEIN CASE RIBONUCLEOPROTEIN RNA UNCLASSIFIED DRUG Wiedenheft, B. Lander, G.C. Zhou, K. Jore, M.M. Brouns, S.J.J. Van Der Oost, J. Doudna, J.A. Doudna, J.A. https://drive.google.com/file/d/127a8PBRy3Qyv2txdjpG_7COpneyzf-uE/view?usp=drivesdk Para ver el documento ingresa a Google con tu cuenta: @cicy.edu.mx Loc REF1 250602s9999 xx |||||s2 |||| ||und|d 26250 26250 0 0 Loc 0 0 F1 CICY CICY RE 2025-06-25 0 B-16136 2025-06-25 16:01:45 2025-06-25 REF1