Letters in 2007

In plants and fungi, cellular ion homeostasis is powered by the proton pump, a member of the P-type ATPase family. The first X-ray structure of the H⁺-ATPase is presented, and insight into the mechanism by which protons are transported against an electrochemical gradient is provided.

The relationship between changes in sea surface temperature and a measure called 'tropical cyclone potential intensity', which provides an upper bound on cyclone intensity, is explored. It is found that changes in potential intensity are closely related to the regional structure of warming, rather than local sea surface temperature — regions that warm more than the tropical average are characterized by increased potential intensity, and vice versa.

The concept of rogue waves in an optical system is investigated by utilizing a new real-time detection technique to study a system that exposes extremely steep, large optical waves as rare outcomes from injection of a population of almost-identical optical pulses. Analysis of these results finds that the optical rogue waves arise when random noise perturbs the initially smooth pulses with a certain frequency shift and within a well-defined time window.

Viral microRNAs have been shown to downregulate complementary viral mRNA targets and to bind to 3′ untranslated regions of host cell mRNAs to prevent their translation or induce their degradation. This paper shows that viral miRNAs can also function as orthologues of cellular miRNAs and downregulate the expression of cellular mRNAs via target sites that may be evolutionary conserved.

Pregnancy makes the instability of upright walking even worse by its constant shifting the centre of gravity. The anatomical adaptations peculiar to female spines that balance the fetal load are detailed, and show that our australopithecine ancestors had much the same adaptations.

Laboratory experiments in microcosms monitoring the hydrocarbon composition of degraded oils are used with carbon isotopic compositions of gas and oil samples taken at wellheads and a Rayleigh isotope fractionation box model to elucidate the mechanisms of hydrocarbon degradation in reservoirs. The data imply a common methanogenic biodegradation mechanism in subsurface degraded oil reservoirs resulting in consistent patterns of hydrocarbon alteration.

Aberration-corrected scanning transmission electron microscopy, coupled with simple imaging simulation, is used to determine with atomic resolution the size, three-dimensional shape, orientation and atomic arrangement of size-selected gold nanoclusters that are preformed in the gas phase and soft-landed on an amorphous carbon substrate.

The protein component of the major urinary protein complex is identified as a potential pheromone ligand mediating male–male aggression via the accessory olfactory pathway.

One of two papers that demonstrate that a single quantum dot placed within an optical cavity can directly block incoming photons when it is strongly coupled to the cavity's optical field. InAs quantum dots placed respectively inside photonic crystal vacancies and inside GaAs microdisks, observe strong coupling directly in the optical transmission signal.

If a stable layer of dense melt formed at the base of the mantle early in Earth's history, it would have undergone slow fractional crystallization and could provide an unsampled geochemical reservoir hosting a variety of incompatible geochemical species (most notably the missing budget of heat producing elements).

One of two papers that demonstrate that a single quantum dot placed within an optical cavity can directly block incoming photons when it is strongly coupled to the cavity's optical field. InAs quantum dots placed respectively inside photonic crystal vacancies and inside GaAs microdisks, observe strong coupling directly in the optical transmission signal.

Evidence for 'supersolidity' has been found in ⁴He from torsional oscillator measurements that suggest some of the solid decouples at low temperatures. Other signatures of superflow have not been seen, but there may be clues in the solid's mechanical behaviour. This study finds large increases in the shear modulus of solid ⁴He at low temperatures that appear closely related to the decoupling seen in the torsional oscillator experiments.

The result of U–Pb dating of minerals in a lunar meteorite, Kalahari 009 is reported. Analyses of five grains associated with basaltic clasts give an age of 4.35 ± 0.15 billion years. These are thought to represent the crystallization ages of parental basalt magma, making Kalahari 009 one of the oldest known mare basalt. This suggests that mare basalt volcanism on the Moon started as early as 4.35 billion years ago.

A combination of novel surface chemistry and fluorescence microscopy allows visualization of dynamic microtubules and plus-end tracking proteins in real time. Three microtubule binding proteins from fission yeast in the in vitro reconstitution system are used, and the results presented yield new insights into the mechanism of plus-end binding proteins in microtubule dynamics.

Bacterial cultures experiencing changes in environmental conditions accumulate mutator strains, presumably to enhance their capability for adaptive evolution. The presence of bacterial viruses is demonstrated to have a similar effect, as during co-evolution of Pseudomonas fluorescens and its lytic DNA phage, bacterial mutation rates significantly increase, resulting in a higher probability of phage extinction.

Observations of Venus' ionosphere reveal strong, circularly-polarized, electromagnetic waves with frequencies near 100 Hz. The waves appear as bursts of radiation lasting 0.25 to 0.5 s and have the expected properties of whistler-mode signals generated by lightning discharges in Venus' clouds.

Experimental results from a study of grain-boundary diffusion of siderophile ('iron-loving') elements through polycrystalline MgO are reported. The diffusivities computed are high enough to allow transport of a number of siderophile elements over geologically significant length scales (tens of kilometres) over the age of the Earth.

Venus' mesosphere is a transition region between the retrograde super rotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere. The mesospheric distributions of HF, HCl, H₂O and HDO are reported, and an unexpected extensive layer of warm air at altitudes 90–120 km on the nightside is found.