A long form (tRNase ZL) of tRNA 3′ processing endoribonuclease (tRNase Z, or 3′ tRNase) can cleave any target RNA at any desired site under the direction of artificial small guide RNA (sgRNA) that mimics a 5′-half portion of tRNA. Based on this enzymatic property, a gene silencing technology has been developed, in which a specific mRNA level can be downregulated by introducing into cells a synthetic 5′-half-tRNA that is designed to form a pre-tRNA-like complex with a part of the mRNA. Recently 5′-half-tRNA fragments have been reported to exist stably in various types of cells, although little is know about their physiological roles. We were curious to know if endogenous 5′-half-tRNA works as sgRNA for tRNase ZL in the cells. Here we show that human cytosolic tRNase ZL modulates gene expression through 5′-half-tRNA. We found that 5′-half-tRNAGlu, which co-immunoprecipitates with tRNase ZL, exists predominantly in the cytoplasm, functions as sgRNA in vitro, and downregulates the level of a luciferase mRNA containing its target sequence in human kidney 293 cells. We also demonstrated that the PPM1F mRNA is one of the genuine targets of tRNase ZL guided by 5′-half-tRNAGlu. Furthermore, the DNA microarray data suggested that tRNase ZL is likely to be involved in the p53 signaling pathway and apoptosis.
Adenine flips out: A combination of X‐ray crystallography, 2‐aminopurine fluorescence labeling, and the use of aminoglycosides as ligands is exploited to demonstrate conformational transitions in the RNA domain that ensures accurate protein synthesis (see picture). The triggering of a conformational change of an adenine unit in the RNA by ligand binding can be used as the basis of a screening method to discover antibiotics.
Lysosomes are thought to be the major intracellular compartment for the degradation of macromolecules. We recently identified a novel type of autophagy, RNautophagy, where RNA is directly taken up by lysosomes in an ATP-dependent manner and degraded. However, the mechanism of RNA translocation across the lysosomal membrane and the physiological role of RNautophagy remain unclear. In the present study, we performed gain- and loss-of-function studies with isolated lysosomes, and found that SIDT2 (SID1 transmembrane family, member 2), an ortholog of the Caenorhabditis elegans putative RNA transporter SID-1 (systemic RNA interference deficient-1), mediates RNA translocation during RNautophagy. We also observed that SIDT2 is a transmembrane protein, which predominantly localizes to lysosomes. Strikingly, knockdown of Sidt2 inhibited up to ˜50% of total RNA degradation at the cellular level, independently of macroautophagy. Moreover, we showed that this impairment is mainly due to inhibition of lysosomal RNA degradation, strongly suggesting that RNautophagy plays a significant role in constitutive cellular RNA degradation. Our results provide a novel insight into the mechanisms of RNA metabolism, intracellular RNA transport, and atypical types of autophagy.
Adenin dreht sich raus: Röntgenkristallographie, Fluoreszenzmarkierung mit 2‐Aminopurin und die Verwendung von Aminoglycosiden als Liganden ermöglichten den Nachweis von Konformationsänderungen an der RNA‐Domäne, die die richtige Proteinsynthese sicherstellt (siehe Bild). Das Auslösen einer Änderung der Konformation einer RNA‐Adenineinheit durch die Bindung von Liganden kann als Grundlage für eine Methode zur Suche nach Antibiotika dienen.
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