Letters in 2009

'Blue straggler' stars lie on or near the main sequence of star clusters and are sufficiently massive that they should have evolved into white dwarfs long ago. Statistical evidence indicates that in globular star clusters the blue stragglers probably form from binary stars. Here, 76 per cent of the blue stragglers in the open cluster NGC 188 are found to be currently in binary systems, a three times higher frequency than that among normal solar-type main-sequence stars.

A longstanding aim in molecular-scale electronics is to create a true transistor analogue in which charge transport through a molecule is directly controlled by external modulation of the molecular orbitals. The observation of such a solid-state molecular device is now reported. The data demonstrate that true molecular transistors can be created, and clear the way for molecularly engineered electronic devices.

Coastal ecosystems are sensitive to changes in the quantity and lability of terrigenous dissolved organic matter (DOM) delivered by rivers. The lability of DOM is thought to decrease with age, but this view stems from work in watersheds where terrestrial plant and soil sources dominate streamwater DOM. Here, glaciated watersheds on the Gulf of Alaska are shown to be a source of old but labile dissolved organic matter, suggesting that glacial runoff is an important source of labile reduced carbon to marine ecosystems.

As the climate changes, species will have to move if they are to remain in an area with the same average temperature. Here, this required movement — termed the velocity of temperature change — is quantified. The results indicate management strategies for minimizing biodiversity loss from climate change and suggest that montane landscapes may effectively shelter many species into the next century.

Non-small-cell lung cancers with activating mutations in the epidermal growth factor receptor (EGFR) often show a clinical response to EGFR kinase inhibitors but tend to develop drug-resistance mutations, including the gatekeeper T790M mutation. Here, a new class of EGFR inhibitors is developed; these agents are 30- to 100-fold more potent against EGFR with the T790M mutation, and up to 100-fold less potent against wild-type EGFR, than current EGFR inhibitors.

Although magnetic fields have an important role in the evolution of gas clouds in the Galaxy, the strength and orientation of the field in the interstellar medium near the heliosphere has been poorly constrained, with previous estimates varying widely and based on indirect observational inferences or modelling. Measurements of the deflection of the solar wind plasma flows in the heliosheath are now used to determine the magnetic field strength and orientation in the interstellar medium.

'Blue straggler' stars lie on or near the main sequence of star clusters and are sufficiently massive that they should have evolved into white dwarfs long ago. Two possible mechanisms have been proposed for their formation: mass transfer between binary companions and stellar mergers resulting from direct collisions between two stars. Here, two distinct parallel sequences of blue stragglers are reported in the globular cluster M 30, one arising from the evolution of close binaries, the other from direct collisions.

Non-volcanic tremor was discovered nearly a decade ago; however, a thorough explanation of the geologic process responsible for tremor generation has yet to be determined. A robust correlation is now identified between extremely small, tidally induced shear stress parallel to the San Andreas fault and non-volcanic tremor activity near Parkfield, California. Such tremor may represent shear failure on a critically stressed fault in the presence of near-lithostatic pore pressure.

There are now nearly 1,000 completed bacterial and archaeal genomes available, but as most of them were chosen for sequencing on the basis of their physiology, the data are limited by a highly biased phylogenetic distribution. To explore the value added by choosing microbial genomes for sequencing on the basis of their evolutionary relationships, the genomes of 56 species of Bacteria and Archaea selected to maximize phylogenetic coverage are now sequenced and analysed.

The small coding capacity of the influenza A virus demands that the virus use the host cellular machinery for many aspects of its life cycle. An integrated systems approach, based on genome-wide RNA interference screening, is now used to identify 295 cellular cofactors required for early-stage influenza virus replication. Knowledge of these host cell requirements provides further targets that could be pursued for antiviral drug development.

If broken chromosomes arising from DNA double-strand breaks are left unrepaired or incorrectly repaired, they can lead to genomic changes that may result in cell death or cancer. DNA-dependent protein kinase (DNA-PK), which comprises the DNA-PK catalytic subunit (DNA-PKcs) and the heterodimer Ku70/Ku80, has a major role in the repair of double-strand breaks. The crystal structure of human DNA-PKcs is now presented, in which the overall fold is clearly visible.

Innate immune responses are important in the early phases of infection; for example, natural killer cells are innate lymphocytes that rapidly exhibit cytotoxic activities against virus-infected cells and produce various cytokines. Here, a new type of innate lymphocyte is found in a novel lymphoid structure associated with adipose tissues in the peritoneal cavity. These cells, termed FALC (fat-associated lymphoid cluster) cells, produce T_H2 cytokines and support B1 cells.

MCL1 — essential for the survival of stem and progenitor cells of multiple lineages — is unique among pro-survival BCL2 family members in that it is rapidly turned over through the action of ubiquitin ligases. Abnormally high levels of MCL1 are expressed in some cancers, but the mechanism of MCL1 overexpression is not well understood. The deubiquitinase USP9X is now shown to stabilize MCL1 and thereby promote cell survival; this makes it a potential therapeutic target.

Optical near-field microscopies can achieve spatial resolutions beyond the diffraction limit, but they cannot match the atomic-scale resolution of electron microscopy. Here, the development of photon-induced near-field electron microscopy — an ingenious blend of these two imaging modalities — opens the way for direct space-time imaging of localized fields at interfaces and visualization of phenomena related to photonics, plasmonics and nanostructures.

Universal patterns can be observed in many collective human activities, including violence. However, the possibility of universal patterns ranging across wars in the size distribution or timing of within-conflict events has barely been explored. Here, the sizes and timing of violent events within different insurgent conflicts are shown to exhibit remarkable similarities, and a unified model of human insurgency — with an interesting resemblance to financial market models — is proposed.

The Kuiper belt is a remnant of the primordial Solar System. Small, sub-kilometre-sized, Kuiper belt objects elude direct detection, but the signature of their occultations of background stars should be detectable. Analysis of archival data now reveals an occultation by a body with an approximately 500-metre radius at a distance of 45 astronomical units. The detection of only one event reveals a deficit of sub-kilometre-sized Kuiper belt objects and implies that these small bodies are undergoing collisional erosion.

Feedback is one of the most powerful techniques for the control of classical systems. An extension into the quantum domain is desirable as it could allow the production of non-trivial quantum states and protection against decoherence. Here, real-time feedback control of the motion of a single atom trapped in an optical cavity is demonstrated, by using individual probe photons carrying information about the atomic position to activate a dipole laser.

A population of extrasolar planets has been uncovered with minimum masses of 1.9–10 times the Earth's mass, called super-Earths, but atmospheric studies can be precluded by the distance and size of their stars. Here, observations of the transiting planet GJ 1214b are reported; it has a mass 6.55 times that of the Earth and a radius 2.68 times the Earth's radius. The star is small and only 13 parsecs away, permitting the study of the planetary atmosphere with current observatories.

The activating E2f transcription factors induce transcription and drive cells out of quiescence, but whether activating E2fs are necessary for normal division is an area of debate. Here, the mouse retina is genetically manipulated to address E2f function in normal cells in vivo. Cells in the mouse retina can still divide in the absence of E2f1–3, although loss of activating E2fs leads to elevated apoptosis; thus, E2fs are not universally required for normal mammalian cell division.

A number of lines of evidence suggest that some crustal faults are weak compared to laboratory measurements of frictional strength; however, a satisfactory explanation for this weakness has remained elusive. Laboratory evidence is now provided for a brittle, frictional weakening mechanism based on common fault zone fabrics. Fault samples with well-developed foliation are shown to be extremely weak compared to their powdered equivalents.