Dissociation of polyoma virus by the chelation of calcium ions found associated with purified virions

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Abstract
Analysis of polyoma virions by X-ray fluorometry demonstrated that Ca2+ was associated with the purified virion. Treatment of purified virions with ethyleneglycol-bis-N,N''-tetraacetic acid (EGTA), which chelates Ca2+ and the reducing agent dithiothreitol, caused the virions to dissociate. EM revealed that the virions were dissociated to the capsomere level. Incubation of polyoma virions with 150 mM NaCl, 10 mM EGTA and 3 mM dithiothreitol was optimum for the dissociation reaction. The pH for the dissociation reaction ranged from 7.5-10.5. CsCl density gradient centrifugation indicated that both EGTA and dithiothreitol were necessary for dissociation to occur; neither reagent alone dissociated the virus. The major protein product fo the dissociated viral particles sedimented at 12S. Relationships between these experiments and the alkaline carbonate-bicarbonate dissociation of polyoma are disscussed.