Involvement of RNase J in CRISPR RNA maturation and degradosome formation in cyanobacteria

Many bacteria and archaea use CRISPR-Cas systems, which provide RNA-based, adaptive, and inheritable immune defenses against invading viruses and other foreign genetic elements. The proper processing of CRISPR guide RNAs (crRNAs) is a crucial step in the maturation of the defense complexes and is frequently performed by specialized ribonucleases encoded by cas genes. However, some systems employ enzymes associated with degradosome or housekeeping functions, such as RNase III or the endoribonuclease RNase E. Here, the endo- and 5´-exoribonuclease RNase J was identified as additional enzyme involved in crRNA maturation, acting jointly with RNase E in the crRNA maturation of a type III-Bv CRISPR-Cas system, and possibly together with a further RNase. Co-IP experiments revealed a small set of proteins that were co-enriched with RNase J, among them PNPase. Despite a measured, strong 3’ exonucleolytic activity of the recombinant enzyme, PNPase was not confirmed to contribute to crRNA maturation. However, the co-IP results indicate that PNPase is a component of the cyanobacterial degradosome that can recruit either RNase E or RNase J, together with additional enriched proteins.