title: Genetic determinants of PAM-dependent DNA targeting and pre-crRNA processing in Sulfolobus islandicus.
abstract: Bacteria and Archaea encode clustered, regularly interspaced, short palindromic repeat (CRISPR) systems to confer adaptive immunity to invasive viruses and plasmids. Recent studies of CRISPR systems revealed that diverse CRISPR-associated (Cas) interference modules often coexist in different organisms but functions of cas genes have not been dissected in any of these systems. The crenarchaeon Sulfolobus islandicus encodes three distinct CRISPR interference modules, including a type IA system and two type IIIB systems: Cmr-α and Cmr-β. To study the genetic determinants of protospacer-adjacent motif (PAM)-dependent DNA targeting activity and mature CRISPR RNA (crRNA) production in this organism, mutants deleting individual genes of the type IA system or removing each of other Cas modules were constructed. Characterization of these mutants revealed that Cas7, Cas5, Cas6, Cas3' and Cas3" are essential for PAM-dependent DNA targeting activity, whereas Csa5, along with all other Cas modules, is dispensable for the targeting in the crenarchaeon. Cas6 is implicated as the only enzyme for pre-crRNA processing and the crRNA maturation is independent of the DNA targeting activity. Importantly, we show that Cas7 and Cas5 are essential for stabilizing the processing intermediates and mature crRNAs, respectively, and that depleting the helicase or nuclease domain of Cas3 leads to the accumulation of processing intermediates. This demonstrates that in addition to Cas6, other Cas proteins of an archaeal type IA system also contribute to crRNA processing.
authors: State Key Laboratory of Agricultural Microbiology and College of Life Science and Technology, Huazhong Agricultural University, Wuhan, China.
authors: Wenfang
authors: W
authors: Peng
authors: Huan
authors: H
authors: Li
authors: Søren
authors: S
authors: Hallstrøm
authors: Nan
authors: N
authors: Peng
authors: Yun Xiang
authors: YX
authors: Liang
authors: Qunxin
authors: Q
authors: She
mesh_terms: D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism*; D064130:CRISPR-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D064113:CRISPR-Cas Systems; D004265:DNA Helicases / Q000235:genetics; D019848:Gene Expression Regulation, Archaeal; D055786:Gene Knockout Techniques; D059372:Nucleotide Motifs; D019642:RNA, Archaeal / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016944:Sulfolobus / Q000235:genetics* / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D064130:CRISPR-Associated Proteins; D019642:RNA, Archaeal; D004265:DNA Helicases
keywords: CRISPR/Cas; Cascade; DNA interference; Sulfolobus islandicus; casmutants; crRNA biogenesis; protospacer-adjacent motifs
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