24 research outputs found

    Hakai is required for stabilization of core components of the m6A mRNA methylation machinery

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    N6-methyladenosine (m6A) is the most abundant internal modification on mRNA which influences most steps of mRNA metabolism and is involved in several biological functions. The E3 ubiquitin ligase Hakai was previously found in complex with components of the m6A methylation machinery in plants and mammalian cells but its precise function remained to be investigated. Here we show that Hakai is a conserved component of the methyltransferase complex in Drosophila and human cells. In Drosophila, its depletion results in reduced m6A levels and altered m6A-dependent functions including sex determination. We show that its ubiquitination domain is required for dimerization and interaction with other members of the m6A machinery, while its catalytic activity is dispensable. Finally, we demonstrate that the loss of Hakai destabilizes several subunits of the methyltransferase complex, resulting in impaired m6A deposition. Our work adds functional and molecular insights into the mechanism of the m6A mRNA writer complex

    Lipid droplet autophagy in the yeast Saccharomyces cerevisiae

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    Cytosolic lipid droplets (LDs) are ubiquitous organelles in prokaryotes and eukaryotes that play a key role in cellular and organismal lipid homeostasis. Triacylglycerols (TAGs) and steryl esters, which are stored in LDs, are typically mobilized in growing cells or upon hormonal stimulation by LD-associated lipases and steryl ester hydrolases. Here we show that in the yeast Saccharomyces cerevisiae, LDs can also be turned over in vacuoles/lysosomes by a process that morphologically resembles microautophagy. A distinct set of proteins involved in LD autophagy is identified, which includes the core autophagic machinery but not Atg11 or Atg20. Thus LD autophagy is distinct from endoplasmic reticulum–autophagy, pexophagy, or mitophagy, despite the close association between these organelles. Atg15 is responsible for TAG breakdown in vacuoles and is required to support growth when de novo fatty acid synthesis is compromised. Furthermore, none of the core autophagy proteins, including Atg1 and Atg8, is required for LD formation in yeast.

    Competition between pairing correlations and deformation from the odd-even mass staggering of francium and radium isotopes

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    The masses of Fr222,224,226-233 and Ra233,234 have been determined with the Penning-trap mass spectrometer ISOLTRAP at the ISOLDE facility at CERN, including the previously unknown mass and half-life of Fr233. We study the evolution of the odd-even staggering of binding energies along the francium and radium isotopic chains and of its lowest-order estimator, Δ3(N). An enhancement of the staggering of Δ3(N) is observed towards neutron number N=146, which points to contributions beyond pairing correlations. These contributions are investigated in the Hartree-Fock and Hartree-Fock-Bogoliubov approaches, emphasizing the connections to the single-particle level density and nuclear deformation. © 2014 American Physical Society.status: publishe

    Masses of exotic calcium isotopes pin down nuclear forces

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    The properties of exotic nuclei on the verge of existence play a fundamental part in our understanding of nuclear interactions. Exceedingly neutron-rich nuclei become sensitive to new aspects of nuclear forces. Calcium, with its doubly magic isotopes (40)Ca and (48)Ca, is an ideal test for nuclear shell evolution, from the valley of stability to the limits of existence. With a closed proton shell, the calcium isotopes mark the frontier for calculations with three-nucleon forces from chiral effective field theory. Whereas predictions for the masses of (51)Ca and (52)Ca have been validated by direct measurements, it is an open question as to how nuclear masses evolve for heavier calcium isotopes. Here we report the mass determination of the exotic calcium isotopes (53)Ca and (54)Ca, using the multi-reflection time-of-flight mass spectrometer of ISOLTRAP at CERN. The measured masses unambiguously establish a prominent shell closure at neutron number N = 32, in excellent agreement with our theoretical calculations. These results increase our understanding of neutron-rich matter and pin down the subtle components of nuclear forces that are at the forefront of theoretical developments constrained by quantum chromodynamics.status: publishe

    Evolution of nuclear ground-state properties of neutron-deficient isotopes around Z=82 from precision mass measurements

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    © 2014 American Physical Society. High-precision mass measurements of neutron-deficient Tl (A=184, 186, 190, 193-195, 198) isotopes as well as Pb (A=202,208), Fr (A=207,208), and Ra (A=224) are performed with the Penning-trap mass spectrometer ISOLTRAP at ISOLDE/CERN. The improved precision of the mass data now allows the study of subtle odd-even effects. The gradual development of collectivity with the removal of protons from the magic Z=82 core is analyzed by combining the new mass results with nuclear charge-radii data and mean-field model predictions.status: publishe

    Mass spectrometry and decay spectroscopy of isomers across the Z=82 shell closure

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    Recent results from a measurement campaign studying the isomerism in neutron-deficient Tl isotopes are presented. The measurements make use of a nuclear spectroscopy setup coupled to the high-resolution Penning-trap mass spectrometer ISOLTRAP at CERN's radioactive ion-beam facility ISOLDE. The mass values of 190,194Tl are improved and a mass-spin-state assignment is carried out. An additional mass measurement of the grandparent nuclide 198At allows the deduction of the spin-state ordering in 190Tl. As a result, the excitation energies of the isomers in both Tl isotopes are determined for the first time to Eex(194Tl)=260(15) keV and E ex(190Tl)=89(12) keV. Furthermore, this allows anchoring of the ground-state and isomer masses of 194Bi, 202Fr, and 206Ac, which are linked by two independent α-decay chains. © 2013 American Physical Society.status: publishe