Structure of the Mengo virion. II. Physicochemical and electron microscopic analysis of degraded virus

Abstract

Incubation of Mengo encephalomyelitis virus at slightly acidic pH in the presence of chloride or bromide ions results in the dissociation of the viral capsid into uniform protein subunits (13.4 S) with the release of the intact viral genome (Mak et al., 1970). Electron microscopic studies have shown that the 13.4 S subunit has a well defined, slightly ellipsoidal shape, with surface dimensions of 16.8 ± 0.3 × 14.2 ± 0.2 nm. It is concluded from these studies that the virus capsid is composed of 12 of these subunits, arranged in icosahedral symmetry. The 13.4 S subunits can be further dissociated into 4.7 S fragments by incubation in 2 M urea. The 4.7 S fragment has an approximately spherical shape, with a diameter of 6.8 ± 0.3 nm; and has the same polypeptide composition as does the 13.4 S subunit. These observations suggest that there are 5 such fragments in each 13.4 S subunit, for a total of 60 in the complete virus capsid. A model is proposed for the architecture of the Mengo virus particle, based on the physicochemical and electron microscopic data obtained for the intact virion and its dissociation products. © 1974.