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Work from the Corey and Rossi labs implicates the Argonaute proteins in transcriptional gene silencing mediated by small RNAs. Shown are argonaut shells secreted by the female octopod Argonauta sp. Photograph by Albert Koetsier. pp 787â792 and 793â797
MicroRNAs (miRNAs) are noncoding small RNAs thought to post-transcriptionally regulate many metazoan genes by binding to partially complementary sites in target messenger RNAs. In this issue, Didiano and Hobert examine known and predicted targets of the nematode lsy-6 miRNA, question the general validity of previously proposed rules about miRNA-target interactions and suggest that many functional miRNA targets might be context dependent, as seen in metazoan gene regulation by transcription factors.
The activation-deactivation cycles of G proteins underlie their key roles as molecular switches for a vast array of biological responses. A study in this issue obtains a first look at how G protein–coupled receptors activate heterotrimeric G proteins to switch on signaling pathways by inducing a specific conformational change within their α subunits.
Controlling the ability of retrotransposons to replicate and reinsert within the genome is important for maintaining the integrity of genetic information. For the first time, it has been shown that naturally occurring small interfering RNAs exist in human cells and derive from the L1 retrotransposon, providing evidence that RNA interference has a role in regulation of retrotransposition in humans.
The structure of Escherichia coli RNase II is the first in the broadly conserved RNB family of exoribonucleases. It explains the catalytic properties of RNase II itself and provides insight into an important eukaryotic RNA degradation and processing complex, the exosome.