August 11, 2000-Using a high-energy x-ray beam to probe fragile crystals of RNA and protein, researchers have obtained the most detailed images ever seen of the factory where amino acids are linked into chainlike proteins.

The studies illuminate the basic structure of the ribosome, a protein-making machine found in all cells. These insights include the first unequivocal proof that the ribosome is a ribozyme, an RNA enzyme.

In two articles published in the August 11, 2000, Science, researchers led by Thomas A. Steitz, a Howard Hughes Medical Institute investigator at Yale University, report that they have obtained the atomic structure of the 50S subunit of the ribosome at a resolution of 2.4 Ångströms. An Ångström is one ten-billionth (10^-10) of a meter.

The ribosome is a large molecular complex of RNA and protein. When ribosomes are isolated from cell extracts, two different fractions are obtained, representing two subunits. The smaller 30S subunit binds the messenger RNA that constitutes the protein's genetic blueprint, as well as the transfer RNA that carries each specific amino acid to be added to the growing chainlike protein molecule. The larger 50S subunit catalyzes the formation of the bond between each amino acid and the growing protein chain.

Steitz and his colleagues at Yale University used the 2.5 billion electron volt x-ray beam at Brookhaven National Laboratory's National Synchrotron Light Source to perform x-ray crystallography on crystals of 50S subunits that were produced with osmium and iridium atoms attached to act as landmarks. Additional data were gathered using the Advanced Photon Source at Argonne National Laboratory.

In x-ray crystallography, protein crystals are bombarded with intense x-ray beams. As the x-rays pass through and bounce off of atoms in the crystal, they leave a diffraction
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
10-Aug-2000