Specificities of and functional coordination between the two Cas6 maturation endonucleases in Anabaena sp. PCC 7120 assign orphan CRISPR arrays to three groups

BioRxiv : the Preprint Server for Biology
Viktoria ReimannWolfgang R Hess


The majority of bacteria and archaea possess an RNA-guided adaptive and inheritable immune system against viruses and other foreign genetic elements that consists of clustered regularly interspaced short palindromic repeats (CRISPRs) and CRISPR-associated (Cas) proteins. In most CRISPR-Cas systems, the maturation of CRISPR-derived small RNAs (crRNAs) is essential for functionality. In some bacteria, multiple instances of cas gene-free (orphan) repeat-spacer arrays exist, while additional instances of arrays that are linked to cas gene cassettes are present elsewhere in the genome. In the cyanobacterium Anabaena sp. PCC 7120, ten CRISPR-Cas repeat-spacer arrays are present, but only two cas gene cassettes plus a Tn7-associated eleventh array are observed. In this study, we deleted the two cas6 genes alr1482 (Type III-D) or alr1566 (Type I-D) and tested the specificities of the two corresponding enzymes in the resulting mutant strains, as recombinant proteins and in a cell-free transcription-translation system. The results assign the direct repeats (DRs) to three different groups. While Alr1566 is specific for one group, Alr1482 has a higher preference for the DRs of the second group but can also cleave those of the first group. ...Continue Reading

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Biologic Segmentation
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Entire Embryo
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