Practice question

RNA-dependent RNA polymerase RdRP amplifies small RNA silencing in plants, nematodes, fungi including fission yeast. Primary siRNAs generated by Dicer recruit RdRP complex RDRC containing Rdp1 polymerase, Hrr1 helicase, Cid12 polyA polymerase via Ago1 to target single-stranded transcripts, synthesizing complementary strand forming dsRNA substrate for secondary Dicer cleavage producing secondary siRNAs distal to trigger. This spreads silencing beyond initial region and maintains signal when trigger diluted. RdRP requires Ago1 slicing providing primer hydroxyl. Amplification explains robust sustainable RNAi in organisms possessing RdRP versus transient silencing in mammals lacking enzyme requiring high synthetic siRNA doses for effective knockdown approaches.