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Publication Abstract from PubMed

Class 2 CRISPR effectors Cas9 and Cas12 may have evolved from nucleases in IS200/IS605 transposons. IscB is about two-fifths the size of Cas9 but shares a similar domain organization. The associated omegaRNA plays the combined role of CRISPR RNA (crRNA) and trans-activating CRISPR RNA (tracrRNA) to guide double-stranded DNA (dsDNA) cleavage. Here we report a 2.78-angstrom cryo-electron microscopy structure of IscB-omegaRNA bound to a dsDNA target, revealing the architectural and mechanistic similarities between IscB and Cas9 ribonucleoproteins. Target-adjacent motif recognition, R-loop formation, and DNA cleavage mechanisms are explained at high resolution. omegaRNA plays the equivalent function of REC domains in Cas9 and contacts the RNA-DNA heteroduplex. The IscB-specific PLMP domain is dispensable for RNA-guided DNA cleavage. The transition from ancestral IscB to Cas9 involved dwarfing the omegaRNA and introducing protein domain replacements.

Structural basis for RNA-guided DNA cleavage by IscB-omegaRNA and mechanistic comparison with Cas9.,Schuler G, Hu C, Ke A Science. 2022 Jun 24;376(6600):1476-1481. doi: 10.1126/science.abq7220. Epub 2022 , May 26. PMID:35617371^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.