CARF-dependent preferential RNA cleavage by Csm6 increases drug susceptibility of mycobacteria

Abstract CRISPR-Cas systems are prokaryotic adaptive immune systems that defend against invading mobile genetic elements. The type III-A CRISPR-Cas system has been studied in the evolutionary and epidemiological context of Mycobacterium tuberculosis, the causative agent of tuberculosis. However, its biological function remains poorly understood. Here, we demonstrate that heterologous expression of csm6, a single-stranded RNA ribonuclease of the CRISPR-Cas system, exhibits preferential RNA cleavage activity targeting host transcripts. This activity significantly downregulates ribosomal and mycolic acid biosynthesis pathway genes, leading to a global reduction in translation levels and an increased drug susceptibility of Mycobacterium smegmatis. Furthermore, mutagenesis analysis revealed that Csm6’s biological function critically depends on its CARF domain rather than its HEPN domain. In conclusion, our study elucidates the biological role of the Csm6 protein in the CRISPR-Cas system, both in vitro and in vivo, highlighting how preferential RNA cleavage impacts multiple mycobacterial processes. These findings provide novel insights into the functional diversity of CRISPR-Cas systems in mycobacteria.