Protein-RNA interplay in translation. Structural studies of RRF, SelB and L1

Abstract: Translation is a central biological process, that is catalysed by a machinery consisting of RNA and protein. In this thesis three different protein components of the bacterial protein synthesis system have been structurally studied. Ribosome recycling factor (RRF) is essential for the recycling step of the translation cycle, elongation factor SelB is a specialised elongation factor needed for co-translational selenocysteine incorporation, and ribosomal protein L1 is a primary binding protein in ribosome assembly. The structure of RRF from Thermotoga maritima was solved by X-ray crystallography. RRF is an L-shaped molecule with size and shape very similar to tRNA. This similarity in combination with data from the literature suggests that RRF can bind similarly to a tRNA to the ribosomal A-site. The structure of a C-terminal, mRNA binding, part of SelB (SelB-C) from Moorella thermoacetica was solved. SelB-C consists of four winged-helix domains arranged into an L-shaped structure. The RNA binding site could be located in the structure based on sequence conservation and data from the literature. Sterical requirements suggest that the L-shape of SelB-C may have to open during the functional interaction with the ribosome. Binding studies were performed with L1 from Thermus thermophilus and a 61-nucleotide fragment of 23S RNA. This protein-RNA complex was crystallised.