Practice question

Argonaute proteins are catalytic core of RISC comprising N, PAZ, MID, PIWI domains. PIWI adopts RNase H-like fold coordinating magnesium ions for endonucleolytic slicing of target RNA complementary to guide. Guide 5' phosphate anchored in MID pocket, 3' end in PAZ, positioning scissile phosphate between nucleotides ten and eleven relative to guide 5' end for cleavage. Human AGO2, Arabidopsis AGO1, fission yeast Ago1 possess slicing activity; other paralogs mediate translational repression. Slicing triggers secondary siRNA biogenesis via RDRC recruitment, coupling post-transcriptional silencing to heterochromatin assembly in centromeres and providing amplification maintaining silencing stability.