DNA targeting by subtype I-D CRISPR-Cas shows type I and type III features
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- DNA targeting by subtype I-D CRISPR-Cas shows type I and type III features
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Prokaryotic CRISPR-Cas immune systems are classified into six types based on their effector complexes which cleave dsDNA specifically (types I, II and V), ssRNA exclusively (type VI) or both ssRNA via a ruler mechanism and ssDNA unspecifically (type III). To date, no specific cleavage of ssDNA target has been reported for CRISPR-Cas. Here, we demonstrate dual dsDNA and ssDNA cleavage activities of a subtype I-D system which carries a type III Cas10-like large subunit, Cas10d. In addition to a specific dsDNA cleavage activity dependent on the HD domain of Cas10d, the helicase Cas3' and a compatible protospacer adjacent motif (PAM), the subtype I-D effector complex can cleave ssDNA that is complementary in sequence to the crRNA. Significantly, the ssDNA cleavage sites occur at 6-nt intervals and the cleavage is catalysed by the backbone subunit Csc2 (Cas7), similar to the periodic cleavage of ssRNA by the backbone subunit of type III effectors. The typical type I cleavage of dsDNA combined with the exceptional 6-nt spaced cleavage of ssDNA and the presence of a type III like large subunit provide strong evidence for the subtype I-D system being an evolutionary intermediate between type I and type III CRISPR-Cas systems.
Original language | English |
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Journal | Nucleic Acids Research |
Volume | 48 |
Issue number | 18 |
Pages (from-to) | 10470-10478 |
Number of pages | 9 |
ISSN | 0305-1048 |
DOIs | |
Publication status | Published - 2020 |
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