Assembly factors in poliovirus morphogenesis.

Extracts of poliovirus-infected HeLa cells promoted the in vitro assembly of 14 S subunits into empty capsids antigenically indistinguishable from procapsids. When infected cells were treated with iodoacetamide, the extract lacked the assembly promoting activity. This activity was restored by the addition of heat-disrupted virions, but the empty capsids formed in this system were antigenically different from procapsids. This and other observations introduce a distinction between the "assembly promoting" and "antigenicity conferring" activities of infected-cell extracts.