Project description:To investigate gene specificity at the level of translation in both the human genome and viruses we devised a high-throughput bicistronic assay to quantify cap-independent translation. We uncover thousands of novel cap-independent translation sequences and provide insights on the landscape of translational regulation in both human and viruses. We find extensive translational elements in the 3â untranslated region (3âUTR) of human transcripts and the polyprotein region of un-capped RNA viruses. Through the characterization of regulatory elements underlying cap-independent translation activity we identify potential mechanisms of secondary structure, short sequence motif and base-pairing with the 18S rRNA. Furthermore, we systematically map the 18S rRNA regions for which reverse complementary enhance translation. Thus we provide insights into the mechanisms of translational control in humans and viruses. high-throughput bicistronic assay for obtaining cap-independent translation measurements of 55,000 fully designed sequences in parallel using fluorescence-activated cell sorting and high-throughput DNA sequencing (FACS-seq).
Project description:In eukaryotes, biogenesis of ribosomes requires folding and assembly of the precursor rRNA (pre-rRNA) with a large number of proteins and snoRNPs into huge RNA-protein complexes. In spite of intense genetic, biochemical and high resolution cryo-EM studies in Saccharomyces cerevisiae, information about the conformation of the earliest 35S pre-rRNA is limited. To overcome this, we performed high-throughput SHAPE chemical probing on the 35S pre-rRNA associated with 90S pre-ribosomes. We focused our analyses on external (5´ETS) and internal (ITS1) transcribed spacers as well as the 18S region. We show that in the 35S pre-rRNA, the central region of the 18S is in a more open configuration compared to 20S pre-rRNA and that the central pseudoknot is not formed. The essential ribosome biogenesis protein Mrd1 influences the structure of the 18S part locally and is involved in organizing the central pseudoknot and surrounding structures. Our results demonstrate that the U3 snoRNA dynamically interacts with the 35S pre-rRNA and that Mrd1 is required for disrupting U3 snoRNA base-pairing interactions in the 5'ETS. We propose that the dynamic U3 snoRNA interactions and Mrd1 are essential for establishing the structure of the central region of 18S that is required for processing and 40S subunit function.