Figure 1.

Comparison of the RNAi and CRISPR-Cas pathways. (A) shRNAs are expressed in the nucleus, and transported to the cytoplasm, where they are processed by Dicer into mature siRNA duplexes. siRNA duplexes are subsequently incorporated into the RNA-induced silencing complex (RISC), and one strand of the duplex directs this complex toward complementary mRNA targets that are inactivated by cleavage. (B) CRISPR-Cas13d activity in mammalian cells requires the expression of a CRISPR-RNA (crRNA) and the Cas endonuclease to form a complex that targets complementary RNA. Complementary RNA targets are inactivated by Cas cleavage. RNA cleavage is mediated by two nuclease domains (HEPNs; shown as two scissors).