@Article{Reimann_Alkhnbashi_Saunders-Struc_const_and-NAR2016,
  author =	 {Reimann, Viktoria and Alkhnbashi, Omer S. and Saunders, 
                  Sita J. and Scholz, Ingeborg and Hein, Stephanie and 
                  Backofen, Rolf and Hess, Wolfgang R.},
  title =	 {Structural constraints and enzymatic promiscuity in the 
                  {Cas6}-dependent generation of {crRNAs}},
  journal =	 NAR,
  year =	 {2016},
  volume =	 {},
  number =	 {},
  pages =	 {},
  user =	 {alkhanbo},
  pmid =	 {27599840},
  doi = 	 {10.1093/nar/gkw786},
  issn = 	 {1362-4962},
  issn = 	 {0305-1048},
  abstract =	 {A hallmark of defense mechanisms based on clustered 
                  regularly interspaced short palindromic repeats (CRISPR) and 
                  associated sequences (Cas) are the crRNAs that guide these 
                  complexes in the destruction of invading DNA or RNA. Three 
                  separate CRISPR-Cas systems exist in the cyanobacterium 
                  Synechocystis sp. PCC 6803. Based on genetic and 
                  transcriptomic evidence, two associated endoribonucleases, 
                  Cas6-1 and Cas6-2a, were postulated to be involved in crRNA 
                  maturation from CRISPR1 or CRISPR2, respectively. Here, we 
                  report a promiscuity of both enzymes to process in vitro not 
                  only their cognate transcripts, but also the respective 
                  non-cognate precursors, whereas they are specific in vivo 
                  Moreover, while most of the repeats serving as substrates 
                  were cleaved in vitro, some were not. RNA structure 
                  predictions suggested that the context sequence surrounding 
                  a repeat can interfere with its stable folding. Indeed, 
                  structure accuracy calculations of the hairpin motifs within 
                  the repeat sequences explained the majority of analyzed 
                  cleavage reactions, making this a good measure for 
                  predicting successful cleavage events. We conclude that the 
                  cleavage of CRISPR1 and CRISPR2 repeat instances requires a 
                  stable formation of the characteristic hairpin motif, which 
                  is similar between the two types of repeats. The influence 
                  of surrounding sequences might partially explain variations 
                  in crRNA abundances and should be considered when designing 
                  artificial CRISPR arrays.}
}