Project description:MALAT1 lncRNA plays key roles in regulating transcription, splicing, and tumorigenesis. Its maturation and stabilization require precise processing by RNase P, which simultaneously initiates the biogenesis of a 3′ cytoplasmic mascRNA. mascRNA was proposed to fold into a tRNA-like secondary structure, but lacks eight conserved linking residues required by the canonical tRNA fold. Here, we report crystal structures of human mascRNA before and after processing, which reveal an ultracompact, quasi-tRNA-like structure. Despite lacking all linker residues, mascRNA faithfully recreates the characteristic “elbow” feature of tRNAs to recruit RNase P and ELAC2 for processing, which exhibit distinct substrate specificities. Rotation and repositioning of the D-stem and anticodon regions preclude mascRNA from aminoacylation, avoiding interference with translation. Therefore, a class of metazoan lncRNAs employ a previously unrecognized, unusually streamlined quasi-tRNA architecture to recruit select tRNA-processing enzymes while excluding others, to drive bespoke RNA biogenesis, processing, and maturation.
Project description:We combine genetic perturbation with cryo-electron microscopy (cryo-EM) to establish the mechanism of PTC maturation during human mitoribosome biogenesis. Cryo-EM structures of large mitoribosomal subunit (mtLSU) assembly intermediates purified from GTPBP6-deficient cells reveal that GTPBP5 acts in concert with the methyltransferase domain of the NSUN4-MTERF4 complex to facilitate PTC folding. Addition of recombinant GTPBP6 to these assembly intermediates provides the structural basis for subsequent GTPBP6-mediated late PTC maturation and suggests a sequential order of mtLSU biogenesis. Finally, cryo-EM analysis of 55S mitoribosomes treated with GTPBP6 explains how this protein can adopt a dual role in ribosome biogenesis and recycling. Taken together, these results provide the molecular basis for PTC maturation and establish a hierarchical model for late mitoribosome biogenesis.
Project description:MALAT1, an abundant lncRNA specifically localized to nuclear speckles, regulates alternative-splicing (AS). The molecular basis of its role in AS remains poorly understood. Here, we report three conserved, thermodynamically stable, parallel RNA-G-quadruplexes (rG4s) present in the 3’ region of MALAT1 which regulates this function. Using rG4 domain specific RNA-pull-down followed by mass-spectrometry, RNA-immuno-precipitation and imaging, we demonstrate the rG4 dependent localization of Nucleolin (NCL) and Nucleophosmin (NPM) to nuclear speckles. Specific G-to-A mutations that abolish rG4 structures, results in the localization loss of both the proteins from speckles. Functionally, disruption of rG4 in MALAT1 phenocopies NCL knockdown resulting in altered pre-mRNA splicing of endogenous genes. These results reveal a central role of rG4s within the 3’ region of MALAT1 orchestrating AS.
Project description:Previously, lncRNA Malat1 knockout mice were generated by insertional inactivation. By crossing this line to MMTV-PyMT mammary tumor mouse model, we produced PyMT;Malat1 wild-type (WT) and PyMT;Malat1 knockout (KO). Furthermore, we generated Malat1 transgenic mice by targeting ROSA26 locus and bred them to PyMT;Malat1 knockout mice to produce Malat1-rescued PyMT;Malat1 knockout;Malat1 transgenic animals (TG). Using mammary tumors from the three groups of animals, we performed RNA-Seq analysis to identify differentially up-regulated genes in KO tumors to find novel target genes of YAP-TEAD pathway.