Nature Biotechnology pp 336 - 341 and pp 313 - 314

Antibody sensors have long been the main tool for detecting chemicals and proteins in complex mixtures. But now, pilot studies carried out by Ronald Breaker and his colleagues suggest that sensors based on an entirely different type of molecule-ribonucleic acids (RNAs)-could represent a better alternative.

Breaker and his team set out to build an RNA sensor by engineering several catalytic RNA molecules (ribozymes or RNA switches) that undergo self cleavage on binding a target molecule. After cleavage, the liberated fragment can be detected by virtue of a radioactive tag. The researchers succeeded in attaching seven of these RNA switches to a gold-coated surface, creating a prototype sensor that could detect different target compounds, including a chemical released into a culture medium by a growing bacteria.

Compared with antibodies, the RNA molecules in this sort of sensors could be more stable and much easier to engineer. And if the molecules can be coupled to fluorescent rather than radioactive tags, it could be possible to design arrays that contain 100 or even 1000 switches that can simultaneously detect many different types of chemicals from complex biological pathways. But first, researchers must expand the range of analytes that can be detected, perhaps even to include proteins, as well as increase the sensitivity of the RNA switches to detect lower concentrations of chemicals. Ultimately, RNA sensors of this type could be very useful in research and for diagnostic purposes.

Nature Biotechnology pp 354 - 359 and pp 314 - 315

Biotechnology approaches for increasing natural enzyme diversity promise to provide a whole range of products for use in medicines, environmental clean up, or even laundry detergents. Now, scientists have come up with a variation on an enzyme engineering method called DNA shuffling that has improved the efficiency of an enzyme that removes sulfur from fossil fuels.

Taking a cue from nature, scientists have been learning how to mimic evolution in the test tube to produce novel enzymes with unique and useful properties. However, existing techniques, which create a new gene by exchanging sections of two related genes, yield a limited number of recombined genes.

Wayne Coco and his colleagues have developed a new DNA shuffling technique, called RACHITT, that generates much more genetic diversity. In the RACHITT approach, the top strand of one gene is cut into many small pieces and mixed with the bottom "scaffold" strand of the related gene. Some of the pieces bind to their complementary sequence on the bottom strand, and the gaps between the pieces are filled in by an enzyme that copies the bottom-strand sequence. The result is a "mosaic" gene built from small sections of both genes. The new technique increases the number of crossovers per gene by more than three-fold, greatly improving the chances of creating an enzyme with the desired properties. Using RACHITT, the researchers produced enzymes that remove sulfur from fossil fuels at twice the rate of the natural enzymes.

Nature Biotechnology pp 371 - 374

Although farmers spray pesticides on their crops each year, plants are naturally quite well equipped to protect themselves against pests, such as aphids and caterpillars. In addition to protective bark and tough waxy coatings, plants have tiny glands (called trichomes) through which they secrete chemicals that can deter leaf-crunching insects. By tweaking the manufacture of these chemicals, researchers believe that they can enhance the inherent pest-resistance of many plants.

In the April issue of Nature Biotechnology, George Wagner and his colleagues explain how they identified a key enzyme-a cytochrome P450 enzyme unique to plant trichome glands-that is involved in the production of these natural pesticides. When the team turned down the activity of this enzyme in tobacco plants, the concentration of a diterpene, just one pest-deterring chemical, was elevated around 20-fold. The modified tobacco plants also secreted more of the diterpene through their glands, preventing destructive aphids from attacking and forming colonies.

The technique could be useful for creating naturally pest-resistant plants, and in molecular farming, where plants are "milked" for chemicals useful as medicines and cosmetics.