When incubated at 40 °C, chorioallantoic membranes produce 80 to 200 p.f.u./cell of Newcastle disease virus (NDV), whereas chick embryo cells and mouse L cells produce only 2 to 10 and 0.1 p.f.u./cell, respectively. Under such conditions NDV ‘minus’ strand RNA accumulates in chick embryo cells (as well as in mouse L cells) but not in chorioallantoic membranes.

Lowering the incubation temperature from 40 to 36 °C resulted in delays in virus release by 5 h from chick embryo cells, but by 1 h from chorioallantoic membranes. The maximum rate of virus RNA synthesis was observed at times when the release of progeny virus had been terminated.

When protein synthesis is inhibited by early addition of cycloheximide, some NDV ‘minus’ strand RNA is found in the chick embryo cells but not in the chorioallantoic membranes. When the inhibitor is added later (2 h after virus infection), no virus RNA is labelled in the chick embryo cells, although some ‘plus’ strand RNAs are found labelled in the chorioallantoic membranes.

It is suggested that the observed difference in the permissiveness of various cell types for NDV depends on the amount of some cellular component involved in NDV ‘plus’ strand RNA synthesis.


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