Letters in 2013

The ultraluminous X-ray source M 101 ULX-1 consists of a black hole orbiting a Wolf-Rayet star; optical spectroscopy now shows that the orbital period is 8.2 days, suggesting that the black hole has a mass in the range 5 to 30 solar masses, though the X-ray spectra are unlike what is expected from accretion onto a stellar-mass black hole—accretion must occur from captured stellar wind, which has hitherto been thought to be so inefficient that it could not power an ultraluminous source.

A new approach to accurately determine mutation frequencies with RNA virus populations called circular sequencing (CirSeq) has been developed; a study of the genetic composition of populations of poliovirus shows the fitness landscape for each nucleotide variant in an evolving RNA virus.

Oncogenic Nras in mouse haematopoietic stem cells can increase the probability of cell division in some cells and decrease it in others; this bimodal activity explains how this single pre-leukaemic mutation can increase proliferation without reducing competitiveness by clonally expanding the rapidly dividing cell population and also promoting long-term self-renewal of stem cells.

The mRNAs of higher eukaryotes are extensively modified internally with N⁶-methyladenosine, but the specific functional role of this modification has been unclear; here this modification on mRNA is shown to be recognized by several proteins, the modification and its recognition serve to regulate the RNA’s lifetime.

Engineered dissipation is used to deterministically produce and stabilize entanglement between two trapped-ion quantum bits, independently of their initial states; the entanglement is stabilized even in the presence of experimental noise and decoherence.

Femtosecond crystallography with an X-ray free-electron laser is used to analyse micrometre-sized protein crystals, generating a high-resolution structure of the protein without previous knowledge of what it looks like.

Mitophagy is the elimination of damaged mitochondria by the autophagosome regulated by the ubiquitin ligase, parkin and the kinase PINK1; a genome-wide RNAi screen with high-content microscopy has identified new genes that have an upstream role in parkin translocation to the mitochondria.

RNA adopts vast and complicated secondary structures in the living cell; reported here is a new approach, structure-seq, that characterises RNA structure in vivo on a genome-wide scale at nucleotide resolution and should be applicable to any organism.

An entangled Bell state of two superconducting quantum bits can be stabilized for an arbitrary time using an autonomous feedback scheme, that is, one that does not require a complicated external error-correcting feedback loop.

A comprehensive study into the effects of polymorphisms on gene expression dynamics during a 12-hour development period of Caenorhabditis elegans shows that both cis and trans expression quantitative trait loci (eQTLs) can increase and decrease gene expression, depending on the time point, and that trans eQTLs can act as modifiers of expression during a given period of development.

Chemical analysis of the meteorite NWA 7533 indicates that it may be a Martian regolith breccia and, if so, that the crust of Mars may have formed in the first 100 million years of the planet’s history.

Plant invasions are thought to alter the ecosystem in a way that disadvantages the native species, making re-establishment after eradication difficult; here, on returning to a site at which an invasive plant altered nitrogen-mineralization levels several decades ago, mineralization is found to have returned to pre-invasion levels, although these new conditions favour new invaders over the natives.

Draft genomes of two south-central Siberian individuals dating to 24,000 and 17,000 years ago show that they are genetically closely related to modern-day western Eurasians and Native Americans but not to east Asians; the results have implications for our understanding of the origins of Native Americans.

There are many uses for surfaces that can stay dry, self-clean or resist icing, and many applications benefit from minimizing the contact time between a surface and any drops that may come into contact with it; drops are now shown to bounce off faster when using a superhydrophobic surface with a morphology that redistributes the liquid mass so that the centre of the drop assists in the recoil.

Divergent angiocrine signals from liver sinusoidal endothelial cells elicit regeneration after immediate injury and provoke fibrosis after chronic insult.

Secreted C-type lectins protect the intestinal epithelium from Gram-positive bacteria; this study shows that for the C-type lectin RegIIIα, bacterial killing occurs in a two-step process whereby the lectin first binds to bacterial peptidoglycans then oligomerizes on the bacterial membrane to form a permeabilizing pore.

Single-unit recordings and optogenetic manipulations in mice undergoing auditory fear conditioning show that fear expression is related to the phasic inhibition of prefrontal cortex (PFC) parvalbumin interneurons; inhibition disinhibits PFC projection neurons and synchronizes their firing, leading to fear expression.

Small molecules are developed that irreversibly bind to the common G12C mutant of K-Ras but not the wild-type protein; crystallographic studies reveal the formation of an allosteric pocket that is not apparent in previous Ras studies, and the small molecules shift the affinity of K-Ras to favour GDP over GTP.

An exactly solvable information-theoretical model of communications with a fully quantum electromagnetic field yields explicit expressions for all point-to-point capacities—the maximum possible rates of data transmission—of noisy quantum channels, with implications for quantum key distribution and fibre-optic communications.

Botulinum neurotoxin A (BoNT/A) is considered the most toxic substance known but is also used as a therapeutic drug for a growing number of diseases and conditions; researchers have now obtained a high-resolution crystal structure of the receptor-binding domain of the BoNT/A in complex with the luminal domain of synaptic vesicle protein 2C (SV2C), one of its receptors, allowing the identification of a peptide that can inhibit complex formation.