Answer :
The enzyme that cuts double-stranded RNAi precursors to 21-25 base-pair segments is Dicer.
Dicer is responsible for processing the RNAi precursors into shorter segments that can be used by the RNA-induced silencing complex (RISC) to target specific mRNA molecules for degradation or translational repression. Dicer plays a pivotal role in the initiation of RNA silencing by recognizing double-stranded RNAs (dsRNAs) and cleaving them into small RNAs using its RNase III-like double-stranded RNA-specific nuclease activities. Small RNAs are largely classified into two groups: small-interfering RNAs (siRNAs) and microRNAs. Dicer is classified as a class IV RNase III enzyme, and, in humans, it contains a helicase domain, two RNase III domains, two dsRBDs, and a Piwi/Ago/Zwille (PAZ) domain.
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