Phosphorus-31 nuclear magnetic resonance study of internal motion in ribonucleic acid of southern bean mosaic virus

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Abstract
31P-NMR spectroscopy was used to study southern bean mosaic virus (SBMV) in its native and EDE treated forms at various pH values in the range 4.5-9.0. The degree of swelling in the latter form is a critical function of pH. Spin-lattice relaxation time (T1), line-width and nuclear Overhauser effect (NOE) measurements were made at 40.51, 80.98 and 190.3 MHz. Evidently, the RNA phosphate groups in native SBMV exhibit low-amplitude internal motions on a nanosecond time scale while the phosphate groups of swollen virus exhibit large-amplitude, more rapid, internal motions. A spread of T1 and NOE values is measured at intermediate stages in the swelling process. The RNA core of the virus appears to undergo a 2 state phase transition from a relatively rigid, compact solid form in the native SBMV to a mobile, solvated state in the fully swollen particle.