Professional Education


  • Bachelor of Science, Ruprecht Karl Universitat Heidelberg (2008)
  • Master of Science, Ruprecht Karl Universitat Heidelberg (2010)
  • Doctor of Philosophy, Ruprecht Karl Universitat Heidelberg (2014)

Stanford Advisors


All Publications


  • An rRNA variant to deal with stress. Nature microbiology Leppek, K., Barna, M. 2019; 4 (3): 382–83

    View details for PubMedID 30787478

  • Author Correction: Functional 5' UTR mRNA structures in eukaryotic translation regulation andhow to find them. Nature reviews. Molecular cell biology Leppek, K., Das, R., Barna, M. 2018

    Abstract

    The legend of Figure 1 has been modified to remove misleading referencing to evolution. The title of the legend has been modified from 'Evolutionary expansion of eukaryotic 5' UTR lengths' to 'Interspecies variation in 5' UTR lengths'; the first sentence of the legend has been modified from 'The length of 5' untranslated regions (UTRs) has increased in eukaryotes during evolution' to 'The length of 5' untranslated regions (UTRs) varies in eukaryotes'. The changes have been made in the HTML and PDF versions of the manuscript.

    View details for PubMedID 30111874

  • The Mammalian Ribo-interactome Reveals Ribosome Functional Diversity and Heterogeneity. Cell Simsek, D., Tiu, G. C., Flynn, R. A., Byeon, G. W., Leppek, K., Xu, A. F., Chang, H. Y., Barna, M. 2017; 169 (6): 1051-1065 e18

    Abstract

    During eukaryotic evolution, ribosomes have considerably increased in size, forming a surface-exposed ribosomal RNA (rRNA) shell of unknown function, which may create an interface for yet uncharacterized interacting proteins. To investigate such protein interactions, we establish a ribosome affinity purification method that unexpectedly identifies hundreds of ribosome-associated proteins (RAPs) from categories including metabolism and cell cycle, as well as RNA- and protein-modifying enzymes that functionally diversify mammalian ribosomes. By further characterizing RAPs, we discover the presence of ufmylation, a metazoan-specific post-translational modification (PTM), on ribosomes and define its direct substrates. Moreover, we show that the metabolic enzyme, pyruvate kinase muscle (PKM), interacts with sub-pools of endoplasmic reticulum (ER)-associated ribosomes, exerting a non-canonical function as an RNA-binding protein in the translation of ER-destined mRNAs. Therefore, RAPs interconnect one of life's most ancient molecular machines with diverse cellular processes, providing an additional layer of regulatory potential to protein expression.

    View details for DOI 10.1016/j.cell.2017.05.022

    View details for PubMedID 28575669

  • Functional 5' UTR mRNA structures in eukaryotic translation regulation and how to find them. Nature reviews. Molecular cell biology Leppek, K., Das, R., Barna, M. 2017

    Abstract

    RNA molecules can fold into intricate shapes that can provide an additional layer of control of gene expression beyond that of their sequence. In this Review, we discuss the current mechanistic understanding of structures in 5' untranslated regions (UTRs) of eukaryotic mRNAs and the emerging methodologies used to explore them. These structures may regulate cap-dependent translation initiation through helicase-mediated remodelling of RNA structures and higher-order RNA interactions, as well as cap-independent translation initiation through internal ribosome entry sites (IRESs), mRNA modifications and other specialized translation pathways. We discuss known 5' UTR RNA structures and how new structure probing technologies coupled with prospective validation, particularly compensatory mutagenesis, are likely to identify classes of structured RNA elements that shape post-transcriptional control of gene expression and the development of multicellular organisms.

    View details for PubMedID 29165424

  • A Distinct, Sequence-Induced Conformation Is Required for Recognition of the Constitutive Decay Element RNA by Roquin. Structure (London, England : 1993) Codutti, L., Leppek, K., Zálešák, J., Windeisen, V., Masiewicz, P., Stoecklin, G., Carlomagno, T. 2015; 23 (8): 1437–47

    Abstract

    The constitutive decay element (CDE) of tumor necrosis factor α (TNF-α) mRNA (Tnf) represents the prototype of a class of RNA motifs that mediate rapid degradation of mRNAs encoding regulators of the immune response and development. CDE-type RNAs are hairpin structures featuring a tri-nucleotide loop. The protein Roquin recognizes CDE-type stem loops and recruits the Ccr4-Caf1-Not deadenylase complex to the mRNA, thereby inducing its decay. Stem recognition does not involve nucleotide bases; however, there is a strong stem sequence requirement for functional CDEs. Here, we present the solution structures of the natural Tnf CDE and of a CDE mutant with impaired Roquin binding. We find that the two CDEs adopt unique and distinct structures in both the loop and the stem, which explains the ability of Roquin to recognize stem loops in a sequence-specific manner. Our findings result in a relaxed consensus motif for prediction of new CDE stem loops.

    View details for DOI 10.1016/j.str.2015.06.001

    View details for PubMedID 26165594

  • An optimized streptavidin-binding RNA aptamer for purification of ribonucleoprotein complexes identifies novel ARE-binding proteins. Nucleic acids research Leppek, K., Stoecklin, G. 2014; 42 (2): e13

    Abstract

    Determining the composition of messenger ribonucleoprotein (mRNP) particles is essential for a comprehensive understanding of the complex mechanisms underlying mRNA regulation, but is technically challenging. Here we present an RNA-based method to identify RNP components using a modified streptavidin (SA)-binding RNA aptamer termed S1m. By optimizing the RNA aptamer S1 in structure and repeat conformation, we improved its affinity for SA and found a 4-fold repeat of S1m (4×S1m) to be more efficient than the established MS2 and PP7 systems from bacteriophages. We then attached the AU-rich element (ARE) of tumor necrosis factor alpha (TNFα), a well-known RNA motif that induces mRNA degradation, via 4×S1m to a SA matrix, and used the resulting RNA affinity column to purify ARE-binding proteins (BPs) from cellular extracts. By quantitative mass spectrometry using differential dimethyl labeling, we identified the majority of established ARE-BPs and detected several RNA-BPs that had previously not been associated with AREs. For two of these proteins, Rbms1 and Roxan, we confirmed specific binding to the TNFα ARE. The optimized 4×S1m aptamer, therefore, provides a powerful tool for the discovery of mRNP components in a single affinity purification step.

    View details for DOI 10.1093/nar/gkt956

    View details for PubMedID 24157833

    View details for PubMedCentralID PMC3902943

  • Roquin promotes constitutive mRNA decay via a conserved class of stem-loop recognition motifs. Cell Leppek, K., Schott, J., Reitter, S., Poetz, F., Hammond, M. C., Stoecklin, G. 2013; 153 (4): 869–81

    Abstract

    Tumor necrosis factor-α (TNF-α) is the most potent proinflammatory cytokine in mammals. The degradation of TNF-α mRNA is critical for restricting TNF-α synthesis and involves a constitutive decay element (CDE) in the 3' UTR of the mRNA. Here, we demonstrate that the CDE folds into an RNA stem-loop motif that is specifically recognized by Roquin and Roquin2. Binding of Roquin initiates degradation of TNF-α mRNA and limits TNF-α production in macrophages. Roquin proteins promote mRNA degradation by recruiting the Ccr4-Caf1-Not deadenylase complex. CDE sequences are highly conserved and are found in more than 50 vertebrate mRNAs, many of which encode regulators of development and inflammation. In macrophages, CDE-containing mRNAs were identified as the primary targets of Roquin on a transcriptome-wide scale. Thus, Roquin proteins act broadly as mediators of mRNA deadenylation by recognizing a conserved class of stem-loop RNA degradation motifs.

    View details for DOI 10.1016/j.cell.2013.04.016

    View details for PubMedID 23663784

  • Genome-wide assessment of AU-rich elements by the AREScore algorithm. PLoS genetics Spasic, M., Friedel, C. C., Schott, J., Kreth, J., Leppek, K., Hofmann, S., Ozgur, S., Stoecklin, G. 2012; 8 (1): e1002433

    Abstract

    In mammalian cells, AU-rich elements (AREs) are well known regulatory sequences located in the 3' untranslated region (UTR) of many short-lived mRNAs. AREs cause mRNAs to be degraded rapidly and thereby suppress gene expression at the posttranscriptional level. Based on the number of AUUUA pentamers, their proximity, and surrounding AU-rich regions, we generated an algorithm termed AREScore that identifies AREs and provides a numerical assessment of their strength. By analyzing the AREScore distribution in the transcriptomes of 14 metazoan species, we provide evidence that AREs were selected for in several vertebrates and Drosophila melanogaster. We then measured mRNA expression levels genome-wide to address the importance of AREs in SL2 cells derived from D. melanogaster hemocytes. Tis11, a zinc finger RNA-binding protein homologous to mammalian tristetraprolin, was found to target ARE-containing reporter mRNAs for rapid degradation in SL2 cells. Drosophila mRNAs whose expression is elevated upon knock down of Tis11 were found to have higher AREScores. Moreover high AREScores correlate with reduced mRNA expression levels on a genome-wide scale. The precise measurement of degradation rates for 26 Drosophila mRNAs revealed that the AREScore is a very good predictor of short-lived mRNAs. Taken together, this study introduces AREScore as a simple tool to identify ARE-containing mRNAs and provides compelling evidence that AREs are widespread regulatory elements in Drosophila.

    View details for DOI 10.1371/journal.pgen.1002433

    View details for PubMedID 22242014

    View details for PubMedCentralID PMC3252268

  • Protein synthesis and translational control: at eye level with the ribosome. EMBO reports Leppek, K., Schott, J., Stoecklin, G. 2011; 12 (12): 1214–16

    Abstract

    At the EMBO Conference on 'Protein Synthesis and Translational Control' held in Heidelberg in September 2011, scientists shared their latest findings on the structure and function of the ribosome, mRNA-specific regulation of translation and the numerous quality control mechanisms that ensure accurate protein synthesis.

    View details for DOI 10.1038/embor.2011.224

    View details for PubMedID 22081139

    View details for PubMedCentralID PMC3245708