Summary auto-generated
Rio Bravo (RB) virus is a non-arthropod-borne member of the Flaviviridae family, isolated from Mexican freetail bats and transmitted aerogenically. This study presents the first detailed biochemical and biophysical characterization of a non-arthropod-borne flavivirus. RB virus particles were spherical with 42 nm diameter, banded at 1.18 g/ml sucrose density with a sedimentation coefficient of ~200S, and contained single-stranded RNA of approximately 40S. Electron microscopy revealed enveloped virions with surface projections (peplomers). Loss of infectivity upon treatment with diethyl ether and sodium deoxycholate confirmed the presence of lipid envelopes. The RNA lacked 3' poly(A) tracts, characteristic of flaviviruses. Viral proteins with similarities to known flavivirus proteins were identified: gp52 and gp47 (envelope proteins), gp46 (non-structural protein 1), p25, and gp20 (precursor to membrane protein). Core and membrane proteins were not clearly identified. These physical and biochemical properties closely resemble those of arthropod-borne flaviviruses, confirming RB virus classification within the Flaviviridae family.
Key findings
- Rio Bravo virus exhibits biochemical and biophysical characteristics nearly identical to arthropod-borne flaviviruses despite lacking an arthropod vector, confirming its assignment to Flaviviridae
- The virus is a spherical, 42 nm enveloped particle with 1.18 g/ml buoyant density and 200S sedimentation coefficient, containing single-stranded RNA lacking poly(A) tracts
- Viral proteins identified include envelope glycoproteins (gp52, gp47), non-structural protein 1 (gp46), precursor membrane protein (gp20), and a 25K protein, with electrophoretic and glycosylation patterns consistent with known flavivirus proteins
- The presence of lipid envelopes is demonstrated by sensitivity to lipid solvents diethyl ether and sodium deoxycholate
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Abstract
1 Division of Infectious Diseases, Children's Hospital, 300 Longwood Avenue, Boston, Massachusetts 02115,
2 Department of Immunology, Mayo Clinic, Rochester, Minnesota 55904,
3 Department of Molecular Genetics and Cell Biology, University of Chicago, Kovler Viral Oncology Laboratory, Chicago, Illinois 60637
and4 St Louis University, Department of Obstetrics and Gynecology, St Louis, Missouri 63104, U.S.A.
Rio Bravo (RB) virus has been assigned to the family Flaviviridae on the basis of its antigenic relatedness to other members of this family. RB virus, unlike most members of the Flaviviridae, is believed not to have an arthropod vector. We examined biochemical and biophysical characteristics of RB virus to determine whether it should be assigned to the Flaviviridae and to compare it with arthropod-borne flaviviruses. Purified RB virus banded at a density of 1.18 g/ml in sucrose and had a sedimentation coefficient of about 200 S. Virions, negatively stained with ammonium molybdate, were spherical, had diameters of 42 nm, and appeared to be surrounded by envelopes bearing surface projections. The loss of infectivity after infectious virus was incubated with diethyl ether or sodium deoxycholate confirmed the presence of envelopes. Partially purified RB virions contained single-stranded RNA, lacking 3' poly(A) tracts, that sedimented in a 15% to 30% sucrose gradient as one discrete band with a sedimentation coefficient of about 40 S. Most of the viral proteins in preparations of purified virus and in immunoprecipitates had similar electrophoretic mobilities and glycosylation patterns to known flavivirus proteins. Therefore, they were assigned the following tentative designations using the nomenclature for flavivirus proteins: gp52 and gp47, envelope proteins; gp46, non-structural protein 1;p25, gp20(prM), precursor to membrane protein; gp < 18K. Putative core and membrane proteins were not identified. These physical and biochemical characteristics of RB virus are remarkably similar to those of the arthropod-borne members of the Flaviviridae and they confirm the classification of RB virus in this family. This is the first report of biochemical and physical properties of a non-arthropod-borne member of the Flaviviridae.