The DNA then instructs the bacterium to produce new viruses. So many are produced, in fact, that the E. coli eventually bursts, setting masses of new virus free to infect other cells.
The new detailed images provided by Rossmann's group also reveal a structure slightly different than what scientists had envisioned.
"We found that the baseplate is shaped like a cup or small dome," Rossmann says. "Previously it was believed that the baseplate was a rather flat structure."
The study also is the first to show how the syringe-like tube is situated in the center of the baseplate, positioned in line with the DNA contained in the virus head.
The studies were done at Purdue using X-ray crystallography, a technique often used to study structures such as proteins and viruses, in atomic detail. But the process works only if the substances can be made to form crystals. Crystals are used because the diffraction pattern from one single molecule could be insignificant, but the many individual, identical molecules in a crystal amplify the pattern.
Diffraction patterns are created when an X-ray beam hits a crystal, causing the electrons surrounding each atom to bend the beam. Computers can then be used to interpret this pattern and reconstruct the positions of the atoms.
"Because the structure is so complex, we could not crystallize the entire virus structure at once," Rossmann says. "Instead, we crystallized the various components and gradually pieced together a picture of the structure."
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Contact: Susan Gaidos
sgaidos@purdue.edu
765-494-2081
Purdue University
30-Jan-2002