tRNA Biogenesis, Function & Quality Control
RNA(Phe) with its 13 modified residues highlighted
Work in our lab focuses on tRNA biogenesis, function, and quality control mechanisms in the yeast Saccharomyces cerevisiae. tRNA processing is essential in all organisms, and involves several trimming and splicing steps, as well as numerous modification steps, sophisticated quality control checks and, in eukaryotes, complex patterns of intracellular trafficking. tRNA is central to translation, and a growing yeast cell employs 3 x 106 tRNAs to form 2 x 106 peptide bonds per second on 300,000 ribosomes with an accuracy of ˜1 error/104 peptide bonds. Errors in specific aspects of tRNA processing and modification lead to the neurodegenerative diseases pontocerebellar hypoplasia and familial dysautonomia, mental retardation, and the mitochondrial diseases MELAS and MERFF, as well as learning and developmental defects in C. elegans, and sensitivity to DNA damaging agents in yeast and humans.
Efficient and accurate translation requires that tRNAs have four features. First, all tRNAs require similar overall shape and structure to ensure their participation in translation with more or less equal efficiency. Second, tRNAs have to be different enough to be recognized uniquely by their corresponding tRNA synthetases. Third, tRNAs have to uniquely decode each mRNA codon to achieve high translation accuracy. Fourth, tRNA has to be rugged enough to survive constant use in translation, but flexible enough to withstand the bending and contortions that occur during passage through the ribosome. The large amount of tRNA in an actively growing yeast cell requires synthesis of two molecules of tRNA per second per locus, and very long tRNA lifetimes. All of these features of tRNA are controlled in part by modifications, and work in our laboratory is currently focused on the precise roles of these modifications in maintaining tRNA quality and tRNA function.