Measurement of the Tau Lepton Polarisation at LEP2

A first measurement of the average polarisation P_tau of tau leptons produced in e+e- annihilation at energies significantly above the Z resonance is presented. The polarisation is determined from the kinematic spectra of tau hadronic decays. The measured value P_tau = -0.164 +/- 0.125 is consistent with the Standard Model prediction for the mean LEP energy of 197 GeV.A first measurement of the average polarisation Pτ of tau leptons produced in e + e − annihilation at energies significantly above the Z resonance is presented. The polarisation is determined from the kinematic spectra of tau hadronic decays. The measured value Pτ=−0.164±0.125 is consistent with the Standard Model prediction for the mean LEP energy of 197 GeV.A first measurement of the average polarisation P_tau of tau leptons produced in e+e- annihilation at energies significantly above the Z resonance is presented. The polarisation is determined from the kinematic spectra of tau hadronic decays. The measured value P_tau = -0.164 +/- 0.125 is consistent with the Standard Model prediction for the mean LEP energy of 197 GeV

The SARS-CoV-2 protein NSP2 impairs the silencing capacity of the human 4EHP-GIGYF2 complex

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DNA binding specificities of Escherichia coli Cas1–Cas2 integrase drive its recruitment at the CRISPR locus

International audienceProkaryotic adaptive immunity relies on the capture of fragments of invader DNA (protospacers) followed by their recombination at a dedicated acceptor DNA locus. This integrative mechanism, called adaptation, needs both Cas1 and Cas2 proteins. Here, we studied in vitro the binding of an Escherichia coli Cas1-Cas2 complex to various protospacer and acceptor DNA molecules. We show that, to form a long-lived ternary complex containing Cas1-Cas2, the acceptor DNA must carry a CRISPR locus, and the protospacer must not contain 3΄-single-stranded overhangs longer than 5 bases. In addition, the acceptor DNA must be supercoiled. Formation of the ternary complex is synergistic, in such that the binding of Cas1-Cas2 to acceptor DNA is reinforced in the presence of a protospacer. Mutagenesis analysis at the CRISPR locus indicates that the presence in the acceptor plasmid of the palindromic motif found in CRISPR repeats drives stable ternary complex formation. Most of the mutations in this motif are deleterious even if they do not prevent cruciform structure formation. The leader sequence of the CRISPR locus is fully dispensable. These DNA binding specificities of the Cas1-Cas2 integrase are likely to play a major role in the recruitment of this enzyme at the CRISPR locus

The SARS-CoV-2 protein NSP2 impairs the microRNA-induced silencing capacity of human cells

Abstract The coronavirus SARS-CoV-2 is the cause of the ongoing pandemic of COVID-19. Given the absence of effective treatments against SARS-CoV-2, there is an urgent need for a molecular understanding of how the virus influences the machineries of the host cell. The SARS-CoV-2 generates 16 Non-Structural Proteins (NSPs) through proteolytic cleavage of a large precursor protein. In the present study, we focused our attention on the SARS-CoV-2 protein NSP2, whose role in the viral pathogenicity is poorly understood. Recent proteomic studies shed light on the capacity of NSP2 to bind the 4EHP-GIGYF2 complex, a key factor involved in microRNA-mediated silencing of gene expression in human cells. In order to gain a better understanding of the function of NSP2, we attempted to identify the molecular basis of its interaction with 4EHP-GIGYF2. Our data demonstrate that NSP2 physically associates with the endogenous 4EHP-GIGYF2 complex in the cytoplasm. Using co-immunoprecipitation and in vitro interaction assays, we identified both 4EHP and a central segment in GIGYF2 as binding sites for NSP2. We also provide functional evidence that NSP2 impairs the function of GIGYF2 in mediating mRNA silencing using reporter-based assays, thus leading to a reduced activity of microRNAs. Altogether, these data reveal the profound impact of NSP2 on the post-transcriptional silencing of gene expression in human cells, pointing out 4EHP-GIGYF2 targeting as a possible strategy of SARS-CoV-2 to take over the silencing machinery and to suppress host defenses

DNA binding specificities of Escherichia coli Cas1–Cas2 integrase drive its recruitment at the CRISPR locus

International audienceProkaryotic adaptive immunity relies on the capture of fragments of invader DNA (protospacers) followed by their recombination at a dedicated acceptor DNA locus. This integrative mechanism, called adaptation, needs both Cas1 and Cas2 proteins. Here, we studied in vitro the binding of an Escherichia coli Cas1-Cas2 complex to various protospacer and acceptor DNA molecules. We show that, to form a long-lived ternary complex containing Cas1-Cas2, the acceptor DNA must carry a CRISPR locus, and the protospacer must not contain 3΄-single-stranded overhangs longer than 5 bases. In addition, the acceptor DNA must be supercoiled. Formation of the ternary complex is synergistic, in such that the binding of Cas1-Cas2 to acceptor DNA is reinforced in the presence of a protospacer. Mutagenesis analysis at the CRISPR locus indicates that the presence in the acceptor plasmid of the palindromic motif found in CRISPR repeats drives stable ternary complex formation. Most of the mutations in this motif are deleterious even if they do not prevent cruciform structure formation. The leader sequence of the CRISPR locus is fully dispensable. These DNA binding specificities of the Cas1-Cas2 integrase are likely to play a major role in the recruitment of this enzyme at the CRISPR locus

Cysteine Proteases and Cell Differentiation: Excystment of the Ciliated Protist Sterkiella histriomuscorum

The process of excystment of Sterkiella histriomuscorum (Ciliophora, Oxytrichidae) leads in a few hours, through a massive influx of water and the resorption of the cyst wall, from an undifferentiated resting cyst to a highly differentiated and dividing vegetative cell. While studying the nature of the genes involved in this process, we isolated three different cysteine proteases genes, namely, a cathepsin B gene, a cathepsin L-like gene, and a calpain-like gene. Excystation was selectively inhibited at a precise differentiating stage by cysteine proteases inhibitors, suggesting that these proteins are specifically required during the excystment process. Reverse transcription-PCR experiments showed that both genes display differential expression between the cyst and the vegetative cells. A phylogenetic analysis showed for the first time that the cathepsin B tree is paraphyletic and that the diverging S. histriomuscorum cathepsin B is closely related to its Giardia homologues, which take part in the cyst wall breakdown process. The deduced cathepsin L-like protein sequence displays the structural signatures and phylogenetic relationships of cathepsin H, a protein that is known only in plants and animals and that is involved in the degradation of extracellular matrix components in cancer diseases. The deduced calpain-like protein sequence does not display the calcium-binding domain of conventional calpains; it belongs to a diverging phylogenetic cluster that includes Aspergillus palB, a protein which is involved in a signal transduction pathway that is sensitive to ambient pH

The YTHDF1-3 proteins are bidirectionally influenced by the codon content of their mRNA targets

N6-methyladenosine (m6A) is the most abundant modification in eukaryotic mRNAs and plays critical roles in a broad variety of biological processes. Recognition of m6A by the YTHDF1-3 proteins results in the alteration of the translation efficiency and stability of methylated mRNAs, although their mode of action is still matter of debates. To decode the molecular basis of YTHDF1-3 action in human cells, we performed an unbiased proteomic screen of their full spectrum of interacting proteins using BioID (proximity-dependent biotin identification). Our systematic BioID mapping revealed that each YTHDF protein is a dynamic hub that associates with both mRNA silencing machineries and the translation apparatus. Based on this, we identified a direct interaction between YTHDF2 and the ribosomal protein RACK1, and found that the silencing activity of YTHDF2 is bidirectionally modulated by the codon content of its targeted mRNAs. Using a tethering reporter system that recapitulates this phenomenon, we confirmed that the three YTHDF proteins selectively repress mRNAs enriched in optimal codons, while they activate those enriched in non-optimal codons. Altogether, these results have important implications for understanding the underlying multiplicity of YTHDF1-3 and could reconcile seemingly contradictory data

Redesigning the stereospecificity of tyrosyl-tRNA synthetase

International audienceD-Amino acids are largely excluded from protein synthesis, yet they are of great interest in biotechnology. Unnatural amino acids have been introduced into proteins using engineered aminoacyl-tRNA synthetases (aaRSs), and this strategy might be applicable to D-amino acids. Several aaRSs can aminoacylate their tRNA with a D-amino acid; of these, tyrosyl-tRNA synthetase (TyrRS) has the weakest stereospecificity. We use computational protein design to suggest active site mutations in Escherichia coli TyrRS that could increase its D-Tyr binding further, relative to L-Tyr. The mutations selected all modify one or more sidechain charges in the Tyr binding pocket. We test their effect by probing the aminoacyl-adenylation reaction through pyrophosphate exchange experiments. We also perform extensive alchemical free energy simulations to obtain L-Tyr/D-Tyr binding free energy differences. Agreement with experiment is good, validating the structural models and detailed thermodynamic predictions the simulations provide. The TyrRS stereospecificity proves hard to engineer through charge-altering mutations in the first and second coordination shells of the Tyr ammonium group. Of six mutants tested, two are active towards D-Tyr; one of these has an inverted stereospecificity, with a large preference for D-Tyr. However, its activity is low. Evidently, the TyrRS stereospecificity is robust towards charge rearrangements near the ligand. Future design may have to consider more distant and/or electrically neutral target mutations, and possibly design for binding of the transition state, whose structure however can only be modeled