title: Adaptation and modification of three CRISPR loci in two closely related cyanobacteria.
abstract: An RNA-based screen was performed to reveal a possible evolutionary scenario for the CRISPR-Cas systems in two cyanobacterial model strains. Following the analysis of a draft genome sequence of Synechocystis sp PCC6714, three different CRISPR-Cas systems were characterized that have different degrees of relatedness to another three CRISPR-Cas systems in Synechocystis sp PCC6803. A subtype III-B system was identified that is extremely conserved between both strains. Strong signals in northern hybridizations and the presence of different spacers (but identical repeats) indicated this system to be active, despite the absence of a known endonuclease candidate gene involved in the maturation of its crRNAs in the two strains. The other two systems were found to differ significantly from each other, with different sets of repeat-spacer arrays and different Cas genes. In view of the otherwise very close relatedness of the two analyzed strains, this is suggestive of an unknown mechanism involved in the replacement of CRISPR-Cas cassettes as a whole. Further RNA analyses revealed the accumulation of crRNAs to be impacted by environmental conditions critical for photoautotropic growth. All six systems are associated with a gene for a possible transcriptional repressor. Indeed, we identified one of these genes, sll7009, as encoding a negative regulator specific for the CRISPR1 subtype I-D system in Synechocystis sp PCC6803.
authors.affiliation: Genetics and Experimental Bioinformatics group, Faculty of Biology, University of Freiburg, Freiburg, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Hein
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Scholz
authors.forename: Björn
authors.initials: B
authors.lastname: Voß
authors.forename: Wolfgang R
authors.initials: WR
authors.lastname: Hess
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D064130:CRISPR-Associated Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D064112:Clustered Regularly Interspaced Short Palindromic Repeats; D000458:Cyanobacteria / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D008969:Molecular Sequence Data; D010802:Phylogeny; D012323:RNA Processing, Post-Transcriptional; D012329:RNA, Bacterial / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D064130:CRISPR-Associated Proteins; D012329:RNA, Bacterial
keywords: CRISPR; comparative genomics; crRNA maturation; cyanobacteria; defense mechanisms; transcriptional regulator
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