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Journal of Virology, August 1999, p. 7050-7055, Vol. 73, No. 8
Section of Molecular Biology and Genetics,
Cornell University, Ithaca, New York 14853,1
and Department of Biology, Brookhaven National
Laboratory, Upton, New York 119732
Received 4 December 1998/Accepted 7 May 1999
The internal structural protein of retroviruses, Gag, comprises
most of the mass of the virion, and Gag itself can give rise to
virus-like particles when expressed in appropriate cells. Previously the stoichiometry of Gag in virions was inferred from indirect measurements carried out 2 decades ago. We now have directly determined the masses of individual particles of the prototypic avian retrovirus, Rous sarcoma virus (RSV), by using scanning transmission electron microscopy. In this technique, the number of scattered electrons in the
dark-field image integrated over an individual freeze-dried virus
particle on a grid is directly proportional to its mass. The RSV
virions had a mean mass of 2.5 × 108 Da,
corresponding to about 1,500 Gag molecules per virion. The population
of virions was not homogeneous, with about one-third to two-thirds of
the virions deviating from the mean by more than 10% of the mass in
two respective preparations. The mean masses for virions carrying
genomes of 7.4 or 9.3 kb were indistinguishable, suggesting that mass
variability is not due to differences in RNA incorporation.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Mass Determination of Rous Sarcoma Virus Virions by
Scanning Transmission Electron Microscopy
*
Corresponding author. Mailing address: Dept. of
Molecular Biology and Genetics, Biotechnology Building, Cornell
University, Ithaca, NY 14853. Phone: (607) 255-2443. Fax: (607)
255-2428. E-mail: vmv1{at}cornell.edu.
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