Letters in 2013

The crystal structure of the Lsm protein ring of the U6 small nuclear ribonucleoprotein (snRNP), with and without an RNA comprising the 3′ end of the U6 small nuclear RNA, is solved here; this structure provides insight into the function of U6 snRNP in precursor messenger RNA splicing.

The El Niño propagation asymmetry (in which sea surface temperature anomalies propagate eastwards during an extreme El Niño event) is shown to be caused by the variations in upper ocean currents in the equatorial Pacific Ocean; increased occurrences of the propagation asymmetry may be a manifestation of global greenhouse warming.

Two proteins are identified in yeast that regulate the timing of pre-ribosome export from the nucleus; Nug2 binds pre-60S particles until they are ready for export, at which time Nug2 is replaced by the export adaptor Nmd3, enabling the export machinery to recognise the pre-ribosome that is ready to be transferred to the cytoplasm.

Plant life-history traits, notably plant investments in growth versus reproduction, can explain the impact of nitrogen:phosphorus stoichiometry on plant species richness; compared with plants in nitrogen-limited communities, plants in phosphorus-limited communities (in which endangered plant species are more common) invest little in phosphorus-intense activity such as sexual reproduction and have conservative leaf traits.

Single magnetic atoms on non-magnetic surfaces have magnetic moments that are usually destabilized within a microsecond, too speedily to be useful, but here the magnetic moments of single holmium atoms on a highly conductive metallic substrate can reach lifetimes of the order of minutes.

The gut microbial metabolite butyrate is shown to induce the differentiation of colonic T regulatory cells in mice and to ameliorate the development of colitis; it also increases histone H3 acetylation at the Foxp3 promoter.

The O-glycosylation enzyme Galnt11 has an important role in heterotaxy, a disorder of left–right body patterning or laterality: Galnt11 modulates Notch signalling which alters cilia types at the embryonic left–right organizer, therefore determining laterality.

A dual-task computer game played by groups of different sizes is used to show that cultural evolution (the maintenance or improvement of cultural knowledge) strongly depends on population size; in larger groups of players, higher cultural complexity and cultural trait diversity are maintained, and improvements to existing cultural traits are more frequent.

Doppler-shifted X-ray emission lines from highly-ionized atoms, appearing together with radio emission from the relativistic jets of the black-hole candidate X-ray binary 4U 1630-47, indicate that the X-ray emission lines arise in a jet travelling at approximately two-thirds the speed of light and imply that the jet contains baryons.

Chemical, isotopic and physical evidence indicate that some of the groundwater in the Chesapeake Bay crater is remnant Early Cretaceous North Atlantic sea water, probably 100–145 million years old, with an average salinity of about 70‰, which is twice that of modern sea water.

This work shows that the Themis protein has a critical role in positive and negative thymocyte selection by dampening responses to low-affinity ligands but without affecting responses to high-affinity ligands, thus enabling positive selection of weakly self-reactive thymocytes.

Two small-molecule disruptors of the glucokinase–glucokinase-regulatory-protein complex, AMG-1694 and AMG-3969, are identified that decrease blood glucose levels in various models of hyperglycaemic rodents.

In mice, provision of butyrate—a short-chain fatty acid produced by commensal microorganisms during starch fermentation—facilitates extrathymic generation and differentiation of Foxp3⁺ regulatory T cells, demonstrating that metabolic by-products are sensed by cells of the immune system and affect the balance between pro- and anti-inflammatory cells.

Most known ferroelectric photovoltaic materials have very wide electronic bandgaps (that is, they absorb only high-energy photons) but here a family of perovskite oxides is described that have tunable bandgaps, allowing their use across the whole visible-light spectrum.

Plants defend themselves against attackers by producing bioactive secondary metabolites such as triterpene saponins; here, the endoplasmic-reticulum-associated degradation (ERAD) system is shown to control the activity of HMGR, the rate-limiting enzyme in the supply of the terpene precursor isopentenyl diphosphate, thereby preventing unrestrained saponin production and ensuring the integrity of plant development.

Growth of a flagellum outside the bacterial cell proceeds by successive subunit acquisition from the cell export machinery to form a chain that is pulled to the flagellum tip, where subunit crystallization provides the entropic force to drive the process.

A chromatin interaction analysis with paired-end tagging (ChIA-PET) approach is used to delineate chromatin interactions mediated by RNA polymerase II in several different stem-cell populations; putative long-range promoter–enhancer interactions are inferred, indicating that linear juxtaposition does not necessarily guide enhancer target selection and prevalent cell-specific enhancer usage.

Two private, heterozygous mutations in two functionally related genes, GUCY1A3 and CCT7, are identified in an extended family with myocardial infarction; these genes encode proteins that work together to inhibit platelet activation after nitric oxide stimulation, suggesting a link between impaired nitric oxide signalling and myocardial infarction risk.

Although olivine was expected to occur within the deep, south-pole basins of asteroid Vesta, which are thought to be excavated mantle rocks, spectral data from NASA’s Dawn spacecraft show that it instead occurs as near-surface materials in Vesta’s northern hemisphere.

Analysis of video records of the Chelyabinsk superbolide of 15 February 2013 show that its orbit was sufficiently similar to the orbit of asteroid 86039 (1999 NC43) to suggest that the two were once part of the same object.