title: The three major types of CRISPR-Cas systems function independently in CRISPR RNA biogenesis in Streptococcus thermophilus.
abstract: CRISPR-Cas systems are small RNA-based immune systems that protect prokaryotes from invaders such as viruses and plasmids. We have investigated the features and biogenesis of the CRISPR (cr)RNAs in Streptococcus thermophilus (Sth) strain DGCC7710, which possesses four different CRISPR-Cas systems including representatives from the three major types of CRISPR-Cas systems. Our results indicate that the crRNAs from each CRISPR locus are specifically processed into divergent crRNA species by Cas proteins (and non-coding RNAs) associated with the respective locus. We find that the Csm Type III-A and Cse Type I-E crRNAs are specifically processed by Cas6 and Cse3 (Cas6e), respectively, and retain an 8-nucleotide CRISPR repeat sequence tag 5' of the invader-targeting sequence. The Cse Type I-E crRNAs also retain a 21-nucleotide 3' repeat tag. The crRNAs from the two Csn Type II-A systems in Sth consist of a 5'-truncated targeting sequence and a 3' tag; however, these are distinct in size between the two. Moreover, the Csn1 (Cas9) protein associated with one Csn locus functions specifically in the production of crRNAs from that locus. Our findings indicate that multiple CRISPR-Cas systems can function independently in crRNA biogenesis within a given organism - an important consideration in engineering coexisting CRISPR-Cas pathways.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, 30602, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Carte
authors.forename: Ross T
authors.initials: RT
authors.lastname: Christopher
authors.forename: Justin T
authors.initials: JT
authors.lastname: Smith
authors.forename: Sara
authors.initials: S
authors.lastname: Olson
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Barrangou
authors.forename: Sylvain
authors.initials: S
authors.lastname: Moineau
authors.forename: Claiborne V C
authors.initials: CV
authors.lastname: Glover
authors.forename: Brenton R
authors.initials: BR
authors.lastname: Graveley
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Terns
authors.forename: Michael P
authors.initials: MP
authors.lastname: Terns
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D064113:CRISPR-Cas Systems; D008957:Models, Genetic; D012329:RNA, Bacterial / Q000378:metabolism*; D017423:Sequence Analysis, RNA; D048249:Streptococcus thermophilus / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D012329:RNA, Bacterial