Research articles

Conjugation of ubiquitin chains onto proteins is an important post-translational modification that regulates the stability, localization and activity of substrate proteins. A series of enzymes known as E1, E2 and E3 mediate assembly of ubiquitin chains but the pathway remains unclear. Theoretical and experimental methodologies are now introduced to study the formation of ubiquitin chains at millisecond time resolution, demonstrating that substrate polyubiquitylation proceeds sequentially.

The Gutenberg–Richter relation and the Omori–Utsu law, both power laws, are two of the long-standing relationships of statistical seismology. Here, aftershock sequences are described according to the faulting style of their main shocks, showing that the time delay before the onset of the power-law aftershock decay rate is on average shorter for thrust main shocks than for normal fault earthquakes. These similar dependences on the faulting style indicate that both the fundamental power laws are governed by the state of stress.

Atomic Bose–Einstein condensates can be used to study many-body phenomena that occur in more complex material systems; however, the charge neutrality of these systems prevents intriguing phenomena that occur for charged particles in a magnetic field. Rotation can be used to create a synthetic magnetic field, but such fields are of limited strength. An optically synthesized magnetic field for ultracold neutral atoms that is not subject to the limitations of rotating systems is now experimentally realized.

Extremely massive stars with initial masses of more than 140 solar masses end their lives when pressure-supporting photons turn into electron–positron pairs, leading to a violent contraction that triggers a nuclear explosion, unbinding the star in a pair-instability supernova. Here, the mass of the exploding core of supernova SN 2007bi is estimated at around 100 solar masses, in which case theory unambiguously predicts a pair-instability supernova. Further observations are well fitted by models of pair-instability supernovae.

The lateral hypothalamic area is the 'feeding centre' in the brain. During fasting, the neuropeptides orexin and melanin-concentrating hormone (MCH) are released in this area and stimulate food intake. The expression of orexin and MCH is now shown to be regulated by the transcription factor Foxa2, a downstream target of insulin signalling. The results show that Foxa2 can act as a metabolic sensor to integrate metabolic signals, adaptive behaviour and physiological responses.

Existing DNA sequence databases carry only a tiny fraction of the total amount of DNA sequence space from bacterial species. Bioinformatics searches of genomic DNA from bacteria commonly identify new noncoding RNAs (ncRNAs) such as riboswitches. Here, an updated computational pipeline is used to discover ncRNAs that rival the known large ribozymes in size and structural complexity; other such RNAs probably remain to be discovered.

Extensive records exist with which to assess the relationship between external climate forcings — such as changes in insolation — and climate variability for middle and high latitudes, but records from equatorial regions are relatively few, especially from regions experiencing the passage of the Intertropical Convergence Zone. A continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa is now presented and analysed.

X-ray crystallography and NMR spectroscopy are two powerful tools to determine the three-dimensional structures and characterize the dynamic properties of proteins. The two methods are now combined to structurally unravel interconverting substrates of a human proline isomerase. Crystallographic approaches are used to define minor protein conformations and, combined with NMR analysis, to show how collective motions contribute to the catalytic power of an enzyme.

Dietary restriction extends healthy lifespan in diverse organisms but reduces fecundity; this is thought to be because of an adaptive reallocation of nutrients from reproduction to somatic maintenance. Here, the nutrients producing the responses of lifespan and fecundity to dietary restriction in Drosophila are identified. Adding essential amino acids to the dietary restriction condition increased fecundity and decreased lifespan; furthermore, addition of methionine alone rescued fecundity.

The learning of novel motor skills through repetitive practice is associated with enhanced synaptic efficacy in the motor cortex. However, how motor learning affects neuronal circuitry at the level of individual synapses and how long-lasting memory is structurally encoded in the intact brain remain unknown. Synaptic connections in the living mouse brain are now shown to respond to motor-skill learning and permanently rewire; this could be the foundation of durable motor memory.

The majority of excitatory neurotransmission in the central nervous system is mediated by ionotropic glutamate receptors, which function by opening a transmembrane ion channel upon binding of glutamate. However, despite this crucial role in neurobiology, the architecture and atomic structure of an intact isotropic glutamate receptor are unknown. The X-ray crystal structure of the rat GluA2 receptor in complex with a competitive antagonist is now reported and analysed.

Type IV secretion systems span the two membranes of Gram-negative bacteria, with three proteins —— VirB7, VirB9 and VirB10 — assembled into a 1.05 megadalton core spanning the inner and outer membranes. Here, the crystal structure of an outer-membrane complex is presented. The structure is the largest determined for an outer-membrane channel and is unprecedented in being composed of three proteins.

Connections between neurons are thought to be remodelled when we learn new tasks or acquire new information; however, it is unclear how neural circuits undergo continuous synaptic changes during learning while maintaining lifelong memories. Here, by following post-synaptic dendritic spines in the mouse cortex, it is shown that a small fraction of new spines induced by novel experience are preserved and provide a structural basis for lifelong memory retention.

The Gulf of California is a part of the world's seafloor-spreading system surrounded by enough seismometers to provide sufficiently high horizontal resolution to address the long-standing debate about the relative importance of dynamic and passive upwelling in the shallow mantle beneath spreading centres. Here, Rayleigh-wave tomography is used to image the shear velocity in the upper 200 kilometres or so of the mantle; the results suggest areas of dynamic upwelling.

Although light is needed for photosynthesis, it can also cause severe oxidative damage. For this reason, protective mechanisms involving feedback-regulated de-excitation of chlorophyll molecules in photosystem II (qE) have evolved. In contrast to flowering plants, little is known about the qE mechanism of eukaryotic algae. Here, a qE-deficient mutant green alga is shown to lack two of the three genes encoding LHCSR, an ancient member of the light-harvesting complex superfamily.

The Agulhas leakage allows the transport of warm and salty Indian Ocean waters into the Atlantic Ocean and provides the main source of heat and salt for the surface branch of the Atlantic meridional overturning circulation. The results of a high-resolution ocean general circulation model now show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to a change in wind forcing.

Heavily doped semiconductors, which can exhibit superconductivity, and low-dimensional superconducting thin films are currently limited by interface scattering, electronic or atomic-scale disorder. Here, the fabrication of a high-quality superconducting layer within a thin-film heterostructure based on SrTiO₃ is reported. By selectively doping a narrow region of SrTiO₃ a two-dimensional superconductor is formed that should provide a model system in which to explore the quantum transport and interplay of both superconducting and normal electrons.

Spintronics aims to represent digital information using spin orientation rather than electron charge, ideally at room temperature and in silicon, which is already ubiquitous in present-day technologies. But so far successful control of spin has only been achieved for electrons and at low temperatures. Now room-temperature injection, manipulation and detection of spin polarization of both electrons and their positively charged counterparts (holes) brings the realization of silicon spintronic devices closer.

Auditory perception can be enhanced or interfered with by visual information from a speaker's face, but previous studies looking at whether tactile information influences speech perception have been limited. Here, by applying inaudible air puffs on participants' skin and thereby mimicking the tiny bursts of aspiration produced by certain speech sounds, it is found that syllables are more likely to be heard as aspirated, demonstrating that tactile information is also integrated in auditory perception.

Accurate transfer RNA (tRNA) aminoacylation is necessary for translational fidelity; however, the accuracy of tRNA aminoacylation in vivo is uncertain. In mammalian cells, approximately 1% of methionine residues used in protein synthesis are now shown to be aminoacylated to non-methionyl-tRNAs. Furthermore, misacylation of methionine increases up to tenfold upon exposing cells to viruses, toll-like receptor ligands or oxidative stress.