@article{Scholz_Lange_Hein-CRISP_Syste_the-2013,
author = {Scholz, Ingeborg and Lange, Sita J. and Hein, Stephanie and 
          Hess, Wolfgang R. and Backofen, Rolf},
title = {{CRISPR}-{Cas} {Systems} in the {Cyanobacterium} 
         {Synechocystis} sp. {PCC6803} {Exhibit} {Distinct} 
         {Processing} {Pathways} {Involving} at {Least} {Two} {Cas6} 
         and a {Cmr2} {Protein}},
journal = {PLoS One},
year = {2013},
doi = {10.1371/journal.pone.0056470},
volume = {8},
user = {sita},
pmid = {23441196},
pages = {e56470},
number = {2},
note = {IS and SJL contributed equally to this work.},
issn = {1932-6203},
abstract = {The CRISPR-Cas (Clustered Regularly Interspaced Short 
            Palindrome Repeats - CRISPR associated proteins) system 
            provides adaptive immunity in archaea and bacteria. A 
            hallmark of CRISPR-Cas is the involvement of short crRNAs 
            that guide associated proteins in the destruction of 
            invading DNA or RNA. We present three fundamentally distinct 
            processing pathways in the cyanobacterium Synechocystis sp. 
            PCC6803 for a subtype I-D (CRISPR1), and two type III 
            systems (CRISPR2 and CRISPR3), which are located together on 
            the plasmid pSYSA. Using high-throughput transcriptome 
            analyses and assays of transcript accumulation we found all 
            CRISPR loci to be highly expressed, but the individual 
            crRNAs had profoundly varying abundances despite single 
            transcription start sites for each array. In a computational 
            analysis, CRISPR3 spacers with stable secondary structures 
            displayed a greater ratio of degradation products. These 
            structures might interfere with the loading of the crRNAs 
            into RNP complexes, explaining the varying abundancies. The 
            maturation of CRISPR1 and CRISPR2 transcripts depends on at 
            least two different Cas6 proteins. Mutation of gene sll7090, 
            encoding a Cmr2 protein led to the disappearance of all 
            CRISPR3-derived crRNAs, providing in vivo evidence for a 
            function of Cmr2 in the maturation, regulation of 
            expression, Cmr complex formation or stabilization of 
            CRISPR3 transcripts. Finally, we optimized CRISPR repeat 
            structure prediction and the results indicate that the 
            spacer context can influence individual repeat structures.}
}