The ribosomal GTPase associated center constitutes the ribosomal area, which is the landing platform for translational GTPases and stimulates their hydrolytic activity. The ribosomal stalk represents a landmark structure in this center, and in eukaryotes is composed of uL11, uL10 and P1/P2 proteins. The modus operandi of the uL11 protein has not been exhaustively studied in vivo neither in prokaryotic nor in eukaryotic cells. Using a yeast model, we have brought functional insight into the translational apparatus deprived of uL11, filling the gap between structural and biochemical studies. We show that the uL11 is an important element in various aspects of 'ribosomal life'. uL11 is involved in 'birth' (biogenesis and initiation), by taking part in Tif6 release and contributing to ribosomal subunit-joining at the initiation step of translation. uL11 is particularly engaged in the 'active life' of the ribosome, in elongation, being responsible for the interplay with eEF1A and fidelity of translation and contributing to a lesser extent to eEF2-dependent translocation. Our results define the uL11 protein as a critical GAC element universally involved in trGTPase 'productive state' stabilization, being primarily a part of the ribosomal element allosterically contributing to the fidelity of the decoding event.

The P-stalk represents a vital element within the ribosomal GTPaseassociated center, which represents a landing platform for translational GTPases. The eukaryotic P-stalk exists as a uL10-(P1-P2) 2 pentameric complex, which contains five identical C-terminal domains, one within each protein, and the presence of only one such element is sufficient to stimulate factor-dependent GTP hydrolysis in vitro and to sustain cell viability. The functional contribution of the P-stalk to the performance of the translational machinery in vivo, especially the role of P-protein multiplication, has never been explored. Here, we show that ribosomes depleted of P1/P2 proteins exhibit reduced translation fidelity at elongation and termination steps. The elevated rate of the decoding error is inversely correlated with the number of the P-proteins present on the ribosome. Unexpectedly, the lack of P1/P2 has little effect in vivo on the efficiency of other translational GTPase (trGTPase)-dependent steps of protein synthesis, including translocation. We have shown that loss of accuracy of decoding caused by P1/P2 depletion is the major cause of translation slowdown, which in turn affects the metabolic fitness of the yeast cell. We postulate that the multiplication of P-proteins is functionally coupled with the qualitative aspect of ribosome action, i.e., the recoding phenomenon shaping the cellular proteome.KEYWORDS ribosomal proteins, ribosomal stalk, ribosome A t the expense of energy from GTP hydrolysis, translational GTPases (trGTPases) confer the unidirectional trajectory for the translational apparatus, providing at the same time unique timing for individual steps (1, 2). The main landing platform for trGTPases is situated on the large ribosomal subunit called the GTPase-associated center (GAC), and it represents a universally conserved ribosomal element where stimulation of trGTPase catalytic activity takes place (3). The GAC consists of two main elements, a conserved fragment of rRNA called the sarcin-ricin loop (SRL) and a ribosomal stalk composed of ribosomal proteins, which form an oligomeric protein complex (4). The protein part of GAC, the ribosome stalk, can be divided into two functionally and evolutionarily distinct parts, the base of the stalk and its lateral elements. The stalk base is composed of conserved ribosomal proteins uL11 (former names L11 and L12 for prokaryotes and eukaryotes, respectively) and uL10 (former names L10 and P0), which anchor the stalk to the rRNA (5, 6). The lateral part of the stalk is built of dimeric complexes P1-P2 in eukaryotes/archaea or (bL12) 2 in prokaryotes (4, 7). Despite the lack of amino acid sequence conservation, the lateral stalk fulfils the same functions and has a similar structural architecture across all domains of life (8). P1/P2 and bL12 proteins are built of two domains. The globular N-terminal domain (NTD) is responsible for dimerization, whereas the highly acidic C-terminal domain (CTD) interacts with trGTPases (9, 10). However, the structure of the CTD in euk...

Fungal infections cause serious problems in many aspects of human life, in particular infections in immunocompromised patients present serious problems. Current antifungal antibiotics target various metabolic pathways, predominantly the cell wall or cellular membrane metabolism. Numerous compounds are available to combat fungal infections, but their efficacy is far from satisfactory and some of them display high toxicity. The emerging antibiotic resistance represents a serious issue as well. Hence, there is a considerable need for new anti-fungal compounds with lower toxicity and higher effectiveness. One of the unique anti-fungal antibiotics is sordarin, the only known compound that acts on the fungal translational machinery per se. Sordarin inhibits protein synthesis at the elongation step of the translational cycle, acting on eukaryotic translation elongation factor 2. In this review, we deliver a robust scientific platform promoting the development of anti-fungal compounds, in particular focusing on the molecular action of sordarin.

The genome-wide duplication event observed in eukaryotes represents an interesting biological phenomenon, extending the biological capacity of the genome at the expense of the same genetic material. For example, most ribosomal proteins in Saccharomyces cerevisiae are encoded by a pair of paralogous genes. It is thought that gene duplication may contribute to heterogeneity of the translational machinery; however, the exact biological function of this event has not been clarified. In this study, we have investigated the functional impact of one of the duplicated ribosomal proteins, uL6, on the translational apparatus together with its consequences for aging of yeast cells. Our data show that uL6 is not required for cell survival, although lack of this protein decreases the rate of growth and inhibits budding. The uL6 protein is critical for the efficient assembly of the ribosome 60S subunit, and the two uL6 isoforms most likely serve the same function, playing an important role in the adaptation of translational machinery performance to the metabolic needs of the cell. The deletion of a single uL6 gene significantly extends the lifespan but only in cells with a high metabolic rate. We conclude that the maintenance of two copies of the uL6 gene enables the cell to cope with the high demands for effective ribosome synthesis.

No abstract