Pervasive generation of oppositely oriented spacers during CRISPR adaptation.

The effect may not be significant for primed adaptation, where most spacers are selected from protospacers with AAG SAM but can become important in the case of unprimed adaptation, which is not only ∼50 times less frequent than primed adaptation ( 28 ), but is also less specific (63% of newly acquired spacers derived from non-AAG protospacers and thus likely leading to non-functional crRNA ( 27 )).

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