Researchers Study Type III-A CRISPR-Cas System as DNA Targeting Modules

The CRISPR-Cas systems provide invader defense in a wide variety of prokaryotes, as well as technologies for gene editing applications. The Type III-A or Csm CRISPR-Cas system is one of the most widely distributed across prokaryotic phyla, and cleaves targeted DNA and RNA molecules.

The team of H. Travis Ichikawa from the University of Georgia constructed modules of Csm systems from Lactococcus lactis, Staphylococcus epidermidis, and Streptococcus thermophilus. The modules include a Cas6 protein and a CRISPR locus for crRNA production, and Csm effector complex proteins. The team expressed these modules in Escherichia coli and evaluated their function. The expressed modules specifically eliminated invading plasmids recognized by their specific crRNAs.

Characteristically, activation of plasmid targeting activity depended on transcription of the plasmid sequence recognized by the crRNA. Moreover, the Csm module can also be programmed to recognize plasmids with novel target sequences by adding appropriate crRNA coding sequences to the module.

These systems provide a platform for evaluation of Type III-A CRISPR-Cas systems in E. coli and for use as programmable transcription-activated DNA targeting system for novel organisms.

For more on this study, read the article in PLOS One.