Molecular analysis of accurate ribosomal translocation

PROJECT SUMMARY In all organisms, proteins are synthesized by ribosomes, large two-subunit enzymes that use aminoacyl- tRNA substrates to translate messenger RNA. Each ribosome is composed of several large RNA molecules (rRNAs) and more than 50 distinct proteins, with rRNA accounting for around two-thirds of the overall mass. Tremendous progress has been made in elucidating the structure of the ribosome and the molecular mechanisms that underpin protein synthesis. Yet, how ribosomes are made in the cell and how components of the ribosome can regulate protein synthesis remain important unresolved questions. The long-term goal of this project is to understand the mechanisms of ribosome biogenesis and regulation in bacteria. Aim 1. In bacteria, the three rRNAs are co-transcribed in long operons. Sequences flanking each rRNA are complementary and form leader-trailer helices (hLTs) in assembly intermediates. These hLTs are absolutely essential for subunit assembly in the cell but dispensable for subunit assembly in the test tube. The proposed work will investigate the cellular function of these key elements. The findings may hold broad relevance for RNA folding and RNA-protein complex assembly inside cells. Aim 2. Protein S21 contributes to the mRNA exit channel of the small subunit. Some bacteria lack S21, other bacteria encode multiple versions, and many bacterial viruses (bacteriophages) encode S21 homologs. The proposed work will investigate the ability of natural S21 variants to substitute for the primary S21 on the ribosome and globally regulate translation. The findings may uncover a widespread mechanism of translational control in bacteria. Ribosomes are a main target of antibiotics, and defects in ribosome biogenesis cause many inherited human diseases (termed ribosomopathies). Insight gained by this project may ultimately lead to the development of novel antimicrobial drugs and/or treatments for one or more hereditary diseases.