PASADENA, Calif.Researchers at the California Institute of Technology (Caltech) have been able, for the first time, to watch viruses infecting individual bacteria by transferring their DNA, and to measure the rate at which that transfer occurs. Shedding light on the early stages of infection by this type of virusa bacteriophagethe scientists have determined that it is the cells targeted for infection, rather than the amount of genetic material within the viruses themselves, that dictate how quickly the bacteriophage's DNA is transferred.
"The beauty of our experiment is we were able to watch individual viruses infecting individual bacteria,"says Rob Phillips, the Fred and Nancy Morris Professor of Biophysics and Biology at Caltech and the principal investigator on the new study. "Other studies of the rate of infection have involved bulk measurements. With our methods, you can actually watch as a virus shoots out its DNA."
The new methods and results are described in a paper titled "A Single-Molecule HersheyChase Experiment," which will appear in the July 24 issue of the journal Current Biology and currently appears online. The lead authors of that paper, David Van Valen and David Wu, completed the work while graduate students in Phillips's group.
In the well-known 1952 Hershey-Chase experiment, Alfred Hershey and Martha Chase of the Carnegie Institution of Washington in Cold Spring Harbor convincingly confirmed earlier claims that DNAand not proteinwas the genetic material in cells. To prove this, the researchers used bacteriophages, which are able to infect bacteria using heads of tightly bundled DNA coated in a protein shell. Hershey and Chase radiolabeled sulfur, contained in the protein shell but not in the DNA, and phosphorous, found in the DNA but not in the protein shell. Then they let the bacteriophages infect the bacterial cells. When they isolated the cells and analyzed their
contents, they found that only t
|Contact: Deborah Williams-Hedges|
California Institute of Technology