Control of translation and mRNA degradation by miRNAs and siRNAs.

The control of translation and mRNA degradation is an important part of the regulation of gene expression. It is now clear that small RNA molecules are common and effective modulators of gene expression in many eukaryotic cells. These small RNAs that control gene expression can be either endogenous or exogenous micro RNAs (miRNAs) and short interfering RNAs (siRNAs) and can affect mRNA degradation and translation, as well as chromatin structure, thereby having impacts on transcription rates.

MicroRNA-dependent localization of targeted mRNAs to mammalian P-bodies.

Small RNAs, including small interfering RNAs (siRNAs) and microRNAs (miRNAs) can silence target genes through several different effector mechanisms. Whereas siRNA-directed mRNA cleavage is increasingly understood, the mechanisms by which miRNAs repress protein synthesis are obscure. Recent studies have revealed the existence of specific cytoplasmic foci, referred to herein as processing bodies (P-bodies), which contain untranslated mRNAs and can serve as sites of mRNA degradation.

Processing bodies require RNA for assembly and contain nontranslating mRNAs.

Recent experiments have defined cytoplasmic foci, referred to as processing bodies (P-bodies), wherein mRNA decay factors are concentrated and where mRNA decay can occur. However, the physical nature of P-bodies, their relationship to translation, and possible roles of P-bodies in cellular responses remain unclear. We describe four properties of yeast P-bodies that indicate that P-bodies are dynamic structures that contain nontranslating mRNAs and function during cellular responses to stress.

An enemy within: fly reconnaissance deploys an endonuclease to destroy nonsense-containing mRNA.

Quality-control mechanisms function in cells to ensure proper gene expression. Nonsense-mediated mRNA decay (NMD) is one such mechanism and it degrades abnormal mRNAs that contain a premature-termination codon. Although NMD is conserved in all eukaryotes that have been examined, it can manifest mechanistic differences in different organisms.

Ccr4p is the catalytic subunit of a Ccr4p/Pop2p/Notp mRNA deadenylase complex in Saccharomyces cerevisiae.

The major pathways of mRNA turnover in eukaryotic cells are initiated by shortening of the poly(A) tail. Recent work has identified Ccr4p and Pop2p as components of the major cytoplasmic deadenylase in yeast. We now demonstrate that CCR4 encodes the catalytic subunit of the deadenylase and that Pop2p is dispensable for catalysis.