Structural basis for Gemin5 decamer-mediated mRNA binding.

Gemin5 in the Survival Motor Neuron (SMN) complex serves as the RNA-binding protein to deliver small nuclear RNAs (snRNAs) to the small nuclear ribonucleoprotein Sm complex via its N-terminal WD40 domain. Additionally, the C-terminal region plays an important role in regulating RNA translation by directly binding to viral RNAs and cellular mRNAs. Here, we present the three-dimensional structure of the Gemin5 C-terminal region, which adopts a homodecamer architecture comprised of a dimer of pentamers. By structural analysis, mutagenesis, and RNA-binding assays, we find that the intact pentamer/decamer is critical for the Gemin5 C-terminal region to bind cognate RNA ligands and to regulate mRNA translation. The Gemin5 high-order architecture is assembled via pentamerization, allowing binding to RNA ligands in a coordinated manner. We propose a model depicting the regulatory role of Gemin5 in selective RNA binding and translation. Therefore, our work provides insights into the SMN complex-independent function of Gemin5.

Amorphous Calcium Carbonate Cluster Nanospheres in Water-Deficient Organic Solvents.

As the key intermediate phase of crystalline calcium carbonate biominerals, amorphous calcium carbonate (ACC) remains mysterious in its structures because of its long-range disorder and instability. We herein report the synthesis of ACC nanospheres in a water-deficient organic solvent system. The obtained ACC nanospheres are very stable under dry conditions. Cryo-TEM reveals that each nanospheres consists of smaller nanosized clusters. We further demonstrate that these clusters can precipitate on other substrates to form an ultrathin ACC coating, which should be an ACC cluster monolayer. The results demonstrate that the presence of small ACC clusters as the subunits of larger aggregates is inherent to ACC synthesized in water-alcohol system but not induced by polymer additives.

Lutimaribacter marinistellae sp. nov., isolated from a starfish.

A taxonomic study was carried out on a Gram-staining-negative bacterium, strain SF-12T, isolated from an unidentified starfish living in Sanya, PR China. Cells of SF-12T were non-spore-forming rods, 0.5-0.8 µm wide, 2.2-2.5 µm long and motile by means of flagella. SF-12T was facultatively anaerobic, heterotrophic, oxidase- and catalase-positive. Growth of SF-12T occurred at 15-38 °C (optimum, 30 °C), at pH 6.5-8.5 (optimum, pH 7.0), and in the presence of 2.0-7.0 % (w/v) NaCl (optimum, 3.0-4.0 %). The predominant fatty acids of SF-12T were C18 : 1ω7c and/or C18 : 1ω6c. Ubiquinone 10 was the sole respiratory quinone of SF-12T. The major polar lipids of SF-12T were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, three unknown aminolipids, and seven unknown phospholipids. The DNA G+C content was 61 mol%. SF-12T showed the highest 16S rRNA gene sequence similarity to Lutimaribacter pacificus W11-2BT (96.06 %), followed by Cribrihabitans neustonicus CC-AMHB-3T (96.02 %), Lutimaribacter saemankumensis SMK-117T (96.0 %), Cribrihabitans marinus CZ-AM5T (95.92 %), Lutimaribacter litoralis KU5D5T (95.92 %) and other species of the family Rhodobacteraceae(<95.9 %). However, phylogenetic trees based on 16S rRNA gene sequences showed that SF-12T formed a lineage with members of the genus Lutimaribacter in the trees. On the basis of phenotypic, chemotaxonomic and phylogenetic analyses, SF-12T is considered to represent a novel species of the genus Lutimaribacter, for which the name Lutimaribacter marinistellae sp. nov. is proposed. The type strain is SF-12T (=MCCC 1K01154T=KCTC 42911T).

Three-dimensional visualization of the Autographa californica multiple nucleopolyhedrovirus occlusion-derived virion envelopment process gives new clues as to its mechanism.

Baculoviruses produce two virion phenotypes, occlusion-derived virion (ODV) and budded virion (BV). ODV envelopment occurs in the nucleus. Morphogenesis of the ODV has been studied extensively; however, the mechanisms underlying microvesicle formation and ODV envelopment in nuclei remain unclear. In this study, we used electron tomography (ET) together with the conventional electron microscopy to study the envelopment of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ODV. Our results demonstrate that not only the inner but also the outer nuclear membrane can invaginate and vesiculate into microvesicles and that intranuclear microvesicles are the direct source of the ODV membrane. Five main events in the ODV envelopment process are summarized, from which we propose a model to explain this process.