A slowly sedimenting infectious component of Rift Valley fever virus

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Abstract
If Rift Valley fever virus (RVF), of which the main component has a sedimentation constant (S20) of about 450, is centrifuged under conditions adequate to secli ment MEF1 poliomyelitis virus (S20 = 156) completely, about 1 % of the original infective particles remain in the supernatant fluid. This slowly sedimenting (S10W) fraction was shown by centrifugation to contain infective components ranging in sedimentation constant from 4 to 19 Svedberg units. Density gradient centrifu gation showed that the densities of these particles varied from 1 to < 1 g./cm. The components were neutralized by RVF immune serum but were not affected by ribonuclease or deoxyribonuclease. In gel diffusion-filtration experiments the S10W virus behaved as substances having very low diffusion constants. Its filtration end-point using graded collodion membranes, is approximately two to three times higher than the ‘whole’ virus. It is suggested that particles comprising the S10W virus fraction contain lipoid material and may be filamentous.The authors wish to express their gratitude to Prof. A. Kipps and R. A. Alexander for their continued interest in this work and to Dr T. H. Mead for many helpful suggestions during preparation of the manuscript.This investigation was supported in part by a Public Health Service research grant Al 04044–02 from the National Institute of Health, Bethesda, U.S.A.