Biochemistry and pathogenicity of echovirus 9 I. Characterization of the virus particles of strains Barty and Hill

Strain Barty, a mouse-pathogenic echovirus 9, which is known to cause epidemic disease in man, and strain Hill, the prototype of echovirus 9, were characterized and compared. Strain Barty virion particles sediment in a low-salt-sucrose gradient with 156 S, whereas particles of the Hill strain form fast-sedimenting aggregates. Plaque formation of the Hill strain is inhibited under an overlay containing agar; virus strain Barty, however, forms plaques. Isoelectric focusing revealed that Barty virion particles exist essentially in one conformation with a characteristic isoelectric point; virions of the Hill strain were found to behave like a mixture of particles with various isoelectric points. Thus, the two echovirus 9 strains, apparently, have a different capsid surface. These divergent capsid surface structures include not only the adsorption site(s)-strain Barty adsorbs less efficiently to cells in culture than strain Hill-but also the determinants inducing neutralizing antibodies: serologically, the two strains are clearly distinguishable. The capsid protein patterns of the two strains in SDS-PAGE show a characteristic difference: VPl of strain Barty is a double band, whereas strain Hill contains a single band in a position just between the two VP1 bands of strain Barty. In addition, fingerprinting to the capsid proteins revealed that the two echovirus 19 strains differ not only in VP1 but probably also in VP3. These determinants of capsid proteins may cause the observed divergent behaviors of the two virus strains, and-possibly-influence pathogenicity.