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18 | NewScientist | 6 April 2013 COMPUTERS made from living cells, anyone? Two groups of researchers have independently built the first biological analogue of the transistor – an integral element of modern electronics. It should make it easier to create gadgets out of living cells, such as biosensors that detect polluted water. A transistor acts as a switch, converting electrical inputs into output signals via logic gates. Now Drew Endy at Stanford University in California and colleagues have designed a transistor-like device that controls the movement of an enzyme called RNA polymerase along a strand of DNA, just as electrical transistors control the flow of current through a circuit. A different enzyme acts as the input, which depending on the sequence of the logic gates, Uranus has its first Trojan asteroid URANUS has a forbidden friend. The first asteroid to share the planet’s orbit has been found, despite claims that Jupiter’s mighty gravity should steal such companions away. The finding hints that more of these asteroids, called Trojans, lurk around unexpected worlds. Since Trojans don’t always stay in place, finding new ones improves our picture of how space rocks migrate around the solar system. Mike Alexandersen of the University of British Columbia in Vancouver, Canada, and colleagues discovered the 60-kilometre-wide Trojan, named 2011 QF99, from an observatory in Hawaii. It lives in a Lagrange point, where the gravitational tugs from the sun and the planet balance out. The asteroid should jitter around in this region for about 70,000 years before becoming unstable enough to be ejected (arxiv.org/abs/1303.5774). Termites revealed as the fairies of the desert IT SEEMS the culprit behind the mysterious “fairy circles” of the Namib desert has been under our noses all along. The fairy circles are discs of barren sand several metres across, surrounded by lush grasses that stand out against the sparse vegetation. A study in 2004 seemed to rule out three theories: radioactive soil, toxic debris left by plants, and termites. But perhaps the researchers didn’t look hard enough. When Norbert Jürgens of the University of Hamburg in Germany examined hundreds of fairy circles in over 2000 kilometres of the Namib desert in southern Africa, GEORGE STEINMETZ/CORBIS IN BRIEF DNA transistor heralds living computers either stops or starts the flow of polymerase. The device can also amplify its flow, another important function of transistors. Because combinations of transistors can carry out computations, this should make it possible to build living gadgets with integrated control circuitry. A similar device has been built by Timothy Lu and colleagues at the Massachusetts Institute of Technology, but amplification gives Endy’s device the edge. he found a species of sand termite, Psammotermes allocerus, was the only organism consistently present. Jürgens observed the insects eating grass roots, killing plants before they could sprout through the soil. With no foliage for water to be transpired from, the water is retained in the ground beneath the patches, helping the termites survive the harsh conditions. The extra water in the soil means that grasses spring up at the boundary of the insects’ circular foraging area, attracting other life (Science, DOI: 10.1126/science.1222999). “This is an amazing phenomenon” but unsurprising, says Nathan Lo from the University of Sydney. In arid regions of northern Australia, termites build mounds that trap nutrients, and an ecosystem develops around them. The circles are “like flattened termite mounds”, he says. AN ARTIFICIAL ovary could make hormone replacement therapy (HRT) a thing of the past. Women with damaged ovaries or who are post-menopausal don’t produce sex hormones, which can lead to osteoporosis. Daily HRT helps, but can have side effects. Emmanuel Opara at Wake Forest University, North Carolina, and colleagues placed two types of hormone-producing cells from rat ovaries inside an algal capsule, then exposed it to chemicals from the pituitary gland that stimulate hormone production. The cells made sex hormones in the same proportions as healthy ovaries (Biomaterials, doi.org/kxv). The hormone capsule would react more dynamically than HRT with fewer side effects, the team say. Fake ovary replaces missing hormones
