Intermediates of the in vitro assembly and disassembly of southern bean mosaic virus.
Southern bean mosaic virus (SBMV) was swollen by treatment with EDTA at pH 7.5 and dissociated into RNA and protein in 1 M NaCl. Aliquots of this preparation were diluted with appropriate buffers to obtain samples in varying concentrations of NaCl, and components of these samples were sedimented through sucrose solutions and dissolved in 0.01 M Tris-HCI buffer, pH 7.5. The protein content and sedimentation properties of components in these preparations were determined. When the NaCl molarity in the treatment exceeded 0.6 M the preparations contained RNA with approximately six protein subunits per SBMV RNA molecule. The protein content of the preparations increased from 30 protein subunits per RNA molecule to 145 protein subunits per RNA molecule as the NaCl molarity used in the treatment was decreased from 0.5 to 0.1 M. The positions of sedimentation of components in these preparations in density gradient centrifugation were intermediate between those of RNA and EDTA-swollen virus. The sedimentation rate of these assembled components increased as the NaCl molarity used in the treatment was decreased. Similar components were assembled when preparations of RNA and protein dissociated from SBMV by dialysis in neutral buffers containing EDTA and 1 M NaCl were diluted to lower NaCl molarities. When SBMV was swollen by treatment with EDTA and dissociated in various concentrations of NaCl, the components formed were similar to those obtained by assembly in the same NaCl molarities. Preparations in the pH 7.5 buffer contained single components which sedimented at 56 S, 55 S, 54 S, 51 S, 46 S, 38 S, 33 S, and 24 S. With the exception of the 24 S component, components formed by disassembly in the same NaCl molarities and dissolved in pH 5.0 buffer sedimented faster.
Tremaine
J H
JH
Research Station, Agriculture Canada, 6660 N. W. Marine Drive, Vancouver, British Columbia, V6T 1X2, Canada.
Ronald
W P
WP
Kelly
E M
EM