The article by Valencia-Sanchez et al. (2006) reviews the mechanisms by which microRNAs (miRNAs) and short interfering RNAs (siRNAs) control translation and mRNA degradation in eukaryotic cells. MiRNAs and siRNAs are small, ~21–26 nucleotide RNA molecules that can modulate gene expression through various mechanisms. The authors discuss how miRNAs and siRNAs can target mRNAs for endonuclease cleavage, leading to their degradation, and how they can also target mRNAs for translation repression. They highlight the role of Argonaute proteins in these processes, particularly the Ago2 protein, which is essential for siRNA-mediated cleavage. The article also explores the involvement of P-bodies, cytoplasmic structures that contain nontranslating mRNAs, in miRNA-mediated regulation. It suggests that miRNAs may increase decapping rates and affect translation initiation, leading to the accumulation of mRNPs in P-bodies. The authors propose an integrated model where miRNAs/RISC complexes interact with specific mRNAs, leading to translation repression and/or increased mRNA decay rates. They also discuss the potential impact of miRNAs on other aspects of RNA metabolism within P-bodies and the broader implications of these findings for understanding gene regulation.The article by Valencia-Sanchez et al. (2006) reviews the mechanisms by which microRNAs (miRNAs) and short interfering RNAs (siRNAs) control translation and mRNA degradation in eukaryotic cells. MiRNAs and siRNAs are small, ~21–26 nucleotide RNA molecules that can modulate gene expression through various mechanisms. The authors discuss how miRNAs and siRNAs can target mRNAs for endonuclease cleavage, leading to their degradation, and how they can also target mRNAs for translation repression. They highlight the role of Argonaute proteins in these processes, particularly the Ago2 protein, which is essential for siRNA-mediated cleavage. The article also explores the involvement of P-bodies, cytoplasmic structures that contain nontranslating mRNAs, in miRNA-mediated regulation. It suggests that miRNAs may increase decapping rates and affect translation initiation, leading to the accumulation of mRNPs in P-bodies. The authors propose an integrated model where miRNAs/RISC complexes interact with specific mRNAs, leading to translation repression and/or increased mRNA decay rates. They also discuss the potential impact of miRNAs on other aspects of RNA metabolism within P-bodies and the broader implications of these findings for understanding gene regulation.