Coupling of ssRNA cleavage with DNase activity in type Ⅲ-A CRISPR-Csm revealed by cryo-E

Coupling of ssRNA cleavage with DNase activity in type Ⅲ-A CRISPR-Csm revealed by cryo-EM and

biochemistry

Minghui Guo;Zhiwei Huang;Kaiming Zhang;Yuwei Zhu;Grigore D.Pintilie;Xiaoyu Guan;Shanshan Li;Michael F.Schmid;Zhuo Ma;Wah Chiu

【期刊名称】《细胞研究（英文版）》 【年(卷),期】2019(029)004

【摘要】The type Ⅲ CRISPR-Cas (clustered regularly interspaced short palindromic repeats-CRISPR-associated genes) systems are bacterially encoded adaptive immune systems for defense against invading nucleic acids.They accomplish this task through the coordinated cleavage of invading substrates of single-stranded RNA and DNA (ssDNA and ssRNA) by the Csm (type Ⅲ-A) or Cmr (type Ⅲll-B) effector complexes.The ssRNA is complementarily bound to the CRISPR RNA (crRNA).However,the structural basis for the DNase and RNase activation of the Csm nucleoprotein complex is largely unknown.Here we report cryo-EM structures of the Csm-crRNA complex,with or without target ssRNA,at near-atomic resolution.Our cryo-EM maps allow us to build atomic models of the key macromolecular components,including Cas10,Csm2,Csm3,Csm4,crRNA and the invading ssRNA.Our structure resolves unambiguously the stoichiometry and tertiary structures of the Csm protein complex and the interactions