Chemical biology: Changing the code

Nature Methods 3, 729–735 (2006)

Can DNA be improved on? Although it is prodigious at encoding genetic information, it does so with an alphabet of only four letters. If this alphabet were extended, more information could be stored.

Ichiro Hirao and Shigeyuki Yokoyama at the RIKEN Genomic Sciences Center in Yokohama, Japan, and their colleagues have prepared unnatural DNA bases that can be incorporated into DNA. Unlike natural bases, which use hydrogen bonds to pair up across the DNA duplex, these unnatural bases form pairs using hydrophobic interactions.

The team showed that standard enzymes, when exposed to the appropriate molecular building blocks, can replicate DNA containing these unnatural base pairs. Such DNA even acts as a template to incorporate unnatural bases into RNA, through translation.

Physics: Muscle power

Opt. Lett. 31, 2610–2612 (2006)

Video monitors of the future might use artificial muscles to get their colours exactly the right shades.

Manuel Aschwanden and Andreas Stemmer of ETH Zurich, Switzerland, have created a variation of a light-spreading device known as a diffraction grating that includes a membrane-like polymer that deforms when a voltage is applied to it. Changing the voltage adjusts the position of the membrane — the artificial muscle — which changes the colour of the diffracted light.

Getting a single pixel to change from blue to red took thousands of volts, but the team hopes to lower the required voltage to commercially viable levels.

Climatology: Methane blast

Credit: E. BROOK

Science 313, 1109–1112 (2006)

The reasons for the marked rise in atmospheric methane concentrations at the end of the last ice age remain controversial.

Hinrich Schaefer of the University of Victoria, Canada, and his colleagues looked at methane trapped in western Greenland ice samples (pictured below) spanning an 800-year period of warming about 12,000 years ago. Compared with present-day atmospheric methane, the gas was less depleted in the heavier carbon isotope carbon-13 than expected. That suggests a different group of sources from today was putting methane into the atmosphere back then.

Emissions from tropical wetlands, or from living plants — a recently discovered source — may account for the discrepancy, the authors say. The fact that the ratio of the isotopes stays the same throughout seems to rule out a burst of methane from clathrates in the sea bed.

Biochemistry: Cold comfort

Curr. Biol. 16, 1591–1605 (2006)

Nerve-endings in the skin that respond to cold temperatures and to chemicals that mimic the cold, such as menthol, could represent the coolest strategy yet for treating chronic pain due to nerve injury. These nerves send signals to the spinal cord that block pain messages from elsewhere in the body.

Susan Fleetwood-Walker of the University of Edinburgh, UK, and her colleagues induced chronic pain in rats, then treated them with either menthol or icilin, another cooling chemical. Both treatments activated the 'coolness' receptor TRPM8 in the skin and had an analgesic effect.

Molecular biology: A question of control

Nature Struct. Mol. Biol. doi: 10.1038/nsmb1138 (2006)

Current methods used to predict which genes are controlled by tiny microRNAs (miRNAs) could be inaccurate, say Dominic Didiano and Oliver Hobert at Columbia University Medical Center in New York.

Genes controlled by miRNAs are typically found by bioinformatic programs, which scour genomic data for short sequences that pair up with a core region of the miRNA molecule. The researchers tested 13 such candidate sites in the worm Caenorhabditis elegans and found that none are controlled by the putative miRNA.

They show that unknown features outside an miRNA's binding site seem to determine whether it controls a gene, and warn that many of the thousands of genes thought to be controlled by miRNAs may need to be re-evaluated.

Biology: Jaws in a flash


Proc. Natl Acad. Sci. USA 103, 12787–12792 (2006)

Super-speedy jaws help an ant of Central and South America in several ways, biologists have found.

High-speed imaging has shown that the trap-jaw ant, Odontomachus bauri (pictured right), can snap its jaws shut at a speed of up to 64 metres per second. The ant can use this motion to stun prey, knock away an enemy, or even fling itself into the air (see news@nature for video at

A team led by Sheila Patek at the University of California in Berkeley and Andrew Suarez at the University of Illinois at Urbana–Champaign says the many uses of the jaw suggests that 'extreme animal movements' can have a number of evolutionary advantages.

Biochemistry: Gut instinct

Science 313, 1126–1130 (2006)

In the bacterial battle for intestinal territory, boundaries are strictly enforced. If the balance is thrown off kilter, this can trigger unpleasant disorders such as inflammatory bowel disease.

Researchers have now identified an antimicrobial protein that may help maintain order. Benign bacteria living in the guts of mice stimulate production of the protein, which binds to sugars protruding from some bacteria, say Lora Hooper and her colleagues at the University of Texas Southwestern Medical Center at Dallas. The mouse protein and its human counterpart rupture the cell walls of unwanted bacteria.

Mouse pups express the gene encoding this protein at particularly high levels after weaning, when intestinal flora change and influxes of antibodies from their mother cease. This suggests that the protein has an innate role in intestinal defence.

Physics: A soft touch

Appl. Phys. Lett. 89, 073501 (2006)

Modifying a kind of electronic transistor could lead to the development of new pressure sensors for prosthetic skin.

Ingrid Graz, based at Johannes Kepler University in Linz, Austria, and her colleagues created the sensors by placing a film of polypropylene ferroelectret, a non-polar material that retains electric charge, on top of a field-effect transistor (FET). The device can detect pressure applied to the film, flipping on or off in response to touch.

The authors suggest that layered arrays of FETs and pressure-sensitive ferroelectrets could be used to create 'sensor skins' for use in prosthetic or wearable electronic devices.

Evolutionary biology: Made for each other

PLoS Biol. 4, e235 (2006)

Parasites, like lovers, are very particular about their relationships. Nicole Gerardo of the University of Arizona and her colleagues report on the specificities that keep parasitic fungi of the genus Escovopsis loyal to their prey, the fungi cultivated by certain ant species.

The parasites are chemically attracted to their hosts in a way in which they are not to other species. The hosts produce antibiotics that, although tolerable to their accustomed parasites, inhibit other closely related species. Only very occasionally are the cultivated fungi susceptible to parasites that they have not previously encountered, making it hard for the parasites to switch hosts.

Astrophysics: A shot in the dark


Nature Phys. doi:10.1038/nphys391 (2006)

Cosmic rays have long been thought to be accelerated to high speeds by exploding stars known as supernovae. But direct evidence has been difficult to come by. Unlike photons, which travel directly from the source, cosmic rays' paths can be twisted by intervening magnetic fields.

Now Michael Stage of the University of Massachusetts in Amherst and his colleagues have caught cosmic rays in the making. Using the Chandra X-ray Observatory, the team identified regions of the Cassiopeia A supernova remnant (pictured) where electrons were being accelerated by the supernova's shockwave. Some electrons were accelerated almost as fast as theoretically possible, and their overall spectrum matched well with cosmic-ray theory.

Journal club

Cole Miller

University of Maryland, College Park, Maryland, USA

Fast-moving stars give this astronomer new reasons to admire the heavens.

I grew up in the countryside, and would often look up at the night sky. Like billions before me, I concluded that the stars are essentially immobile. Indeed, in our vicinity, a typical star moves at only 20 kilometres per second relative to the average motion of nearby stars.

Recently, however, some exceptions to this slow grandeur have been discovered. Warren Brown of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, and his colleagues (W. R. Brown et al. Astrophys. J. 640, L35–L38; 2006) report observations of so-called 'hypervelocity' stars. These stars, tens of thousands of light years away, have speeds of 500–700 kilometres per second, which is sufficient to escape our Galaxy entirely.

Remarkably, the best explanation for the behaviour of these objects was proposed before their discovery (J. G. Hills Nature 331, 687–689; 1988). If a closely bound pair of stars plunges near a supermassive black hole lurking at the galaxy's centre, purely gravitational effects can separate the stellar binary, leaving one star in orbit around the black hole and sending the other on a one-way trip to intergalactic space. A Galactic-Centre origin for these stars is consistent with their current ages, positions and projected velocities.

Even more dramatic ejections could happen when stars interact with the binary supermassive black holes inside recently merged galaxies.

I live in the city now, so the skies are not as favourable for perusal. When I do look up, though, I have a newfound respect for the dynamism of the heavens and the role of black holes in the cosmic dance.