The effect of EDTA and Mg2+ on the infectivity and structure of southern bean mosaic virus.

Abstract Purified preparations of 0.08–0.1 mg/ml of southern bean mosaic virus (SBMV) lost 88–99% or more of their infectivity when incubated at room temperature for 2–3 hours with 0.001 M ethylenediaminetetraacetic acid (EDTA) in phosphate buffer, pH 7. EDTA reduced infectivity more readily at pH 9 than at pH 7, and more readily in 0.001 M than in 0.1 M phosphate buffer, pH 7. Magnesium ions reduced the effect of EDTA on virus infectivity. When 0.01 M MgSO4 was present in the incubating solution, losses due to EDTA were markedly reduced. Preincubation of the virus with Mg2+ prevented infectivity losses from occurring during subsequent EDTA treatments. SBMV treated with EDTA at pH 9 sedimented as two distinct infectious components in sucrose density gradient columns—a lower component corresponding in sedimentation properties to untreated virus, and an upper component with a 260 280 absorption ratio indicating a higher than normal proportion of nucleic acid to protein. The s20,w of untreated SBMV was 114.5, but the major component sedimented at 73 S if the virus (5 mg/ml) was incubated for 12 hours with 0.01 M EDTA, pH 7, and at 98 S if incubated 12 hours with EDTA plus 0.05 M MgSO4. Incubation of virus for 24 hours in 0.01 M EDTA resulted in the appearance of a component sedimenting at 6–25 S, with only a trace of a 73 S component.