How IscB-ωRNA cuts DNA compared to Cas9

A 2.78-angstrom cryo-electron microscopy structure reveals architectural and mechanistic similarities between IscB and Cas9.

• IscB is approximately two-fifths the size of Cas9 but shares a similar domain organization.
• The ωRNA in IscB functions as both CRISPR RNA and trans-activating CRISPR RNA, guiding double-stranded DNA cleavage.
• High-resolution observations detail target-adjacent motif recognition, R-loop formation, and DNA cleavage mechanisms.
• ωRNA performs roles similar to REC domains found in Cas9, interacting with the RNA-DNA heteroduplex.
• The IscB-specific PLMP domain is not required for RNA-guided DNA cleavage.
• The evolution from IscB to Cas9 involved a reduction in ωRNA size and protein domain changes.

Simplified