Abstract
The mechanism of the enhancement by Yaba virus (YV) of poliovirus plaque formation was studied. Poliovirus adsorbed equally well to both YV-infected and normal JINET cells. Infectious RNA of poliovirus was also enhanced in YV-infected cells, thus indicating the step or sequence of steps of poliovirus growth cycle enhanced by YV may be those subsequent to poliovirus uncoating. One-step growth experiments revealed that the final yield and the release of progeny poliovirus were enhanced in YV-infected cells. This may account for the enhancement of the plaque size of poliovirus. The enhancement of the plaque number of the super-infecting virus by YV appeared to result from the interaction between a single YV-infected cell and a single infecting polio virus genome which failed to express its function under ordinary conditions. This enhancement may be brought about by the disturbance by YV of a host cellular defence mechanism other than that mediated by interferon.