Answer :
Final answer:
Dicer is the protein that functions as an endonuclease during the first step of RNA interference, processing dsRNA and pre-microRNA into siRNA or miRNA fragments that interface with RISC for gene silencing.
Explanation:
The protein that acts as an endonuclease in the first step of RNA interference is known as Dicer. This protein cleaves long double-stranded RNAs (dsRNAs) and pre-microRNAs into shorter fragments. These fragments include 21-23 nucleotide long short interfering RNAs (siRNA) or 19-25 nucleotide long microRNAs (miRNA), which are characteristic for having two unpaired nucleotides at the 3' end. Once processed, these RNA fragments bind with the RISC (RNA-induced silencing complex), which then leads to the targeted degradation or translational repression of complementary messenger RNA (mRNA).
