Just as architects usually get more glory than carpenters, DNA is more famous than the molecular machine that converts genetic blueprints into proteins. But the ribosome is in the limelight today with the announcement of this year's Nobel Prize in chemistry.
The prize was awarded to three scientists who revealed the atomic structure and inner workings of the ribosome: Ada Yonath of the Weizmann Institute of Science in Rehovot, Israel; Thomas Steitz of Yale University; and Venkatraman Ramakrishnan of the Medical Research Council Laboratory of Molecular Biology in Cambridge, United Kingdom. All three used a technique known as x-ray crystallography to pinpoint the position of thousands of atoms in the cellular machine known as the ribosome, and all will share one-third of the $1.4 million prize.
"It's a fantastic accomplishment and one that everyone in the field has known for some time is worthy of such recognition," says Wayne Hendrickson, an x-ray crystallographer at Columbia University. Hendrickson adds that this year's prize also completes the Nobel Committee's recognition for the discoverers of biology's central dogma, which describes how genetic information in DNA is copied into RNA, which is then translated into proteins. In 1962, James Watson, Francis Crick, and Maurice Wilkins were awarded the Nobel for their atomic model of DNA. In 2006, Roger Kornberg won for his x-ray structures of RNA polymerase, which translates DNA into RNA. Today's prize for work on the ribosome completes that, Hendrickson says.
Ribosomes exist in all cells in all living organisms. Although central, they are anything but simple. Dozens of different proteins and strands of RNA form a complicated machine divided into two principal components. The smaller component, known as the 30S subunit, works mainly to decode the genetic code in messenger RNA. The larger 50S subunit then takes this information and uses it to stitch together the proper sequence of amino acids that make up the final protein. Early on, researchers struggled to map the atomic structure of even one of these subunits. Producing an x-ray structure requires first creating crystals of millions of copies of a ribosome aligned in near perfect order. If that ordering is precise enough, researchers can then fire a beam of x-rays at the crystal. The pattern in which those x-rays then deflect off the crystal can then be used to map out the arrangement of atoms in the molecule.
In 1980, Yonath managed to generate the first low-quality crystals of a ribosome. By 1990, she had upped the quality of her crystals, but she still struggled to a good structure. Steitz, along with his longtime Yale colleague Peter Moore, jumped into the fray in 1995, following Yonath's recipe for making ribosomal crystals. By 1998, they used additional insights gleaned from electron microscopy studies to help them acquire a low-resolution 9 Angstrom structure of the ribosome. In August, 2000 Steitz's group then published a higher 2.4 Angstrom resolution structure of the large subunit (Science, 11 August 2000, p. 905). Meanwhile, Yonath's and Ramakrishnan's groups published slightly lower resolution structures of the smaller subunit the following month. Since then, the three groups, plus other teams, have used those structures and others to understand in atomic detail how ribosomes translate genetic information into proteins.
The three groups have also begun to push practical applications of their work. All three, for example, have reported crystal structures that show how different antibiotics bind to the ribosome. And several companies are now using these structures in an effort to design new antibiotics against worrisome infections, such as methicillin-resistant Staphylococcus aureus and tuberculosis.
But Steitz, for one, says he never thought initially that anything more than a fundamental insight into the molecular workings of biology would come of the work. "It seemed a bit like trying to climb Mount Everest," Steitz says. "We knew it was doable. But we didn't know how to get there. When we got there in 2000, it was exhilarating. In fact, it was the most exhilarating moment I've had in science."
The original version of the story stated that Roger Kornberg won a 2006 Nobel Prize for his work on DNA polymerase, which translates DNA into RNA. That translation is carried out by RNA polymerase. Kornberg was awarded his Nobel prize for his crystallography work on RNA polymerase. Thanks to several readers for pointing out our error.