On the regulation of protein synthesis in vaccinia virus infected cells.

All eukaryotic mRNA species show a characteristic individual translational efficiency under conditions of restricted polypeptide chain initiation caused by an increase in the osmolarity of the growth medium. In vaccinia virus infected L cells or HeLa cells virus mRNAs can be grouped into classes on the basis of their relative labelling under standard and hypertonic conditions. Under the latter conditions, most of the "early" mRNAs possess very high translational efficiencies, most of the "intermediate" mRNAs show an intermediate efficiency and the most prominent "late" mRNAs show a translational efficiency which is lower than that of other virus mRNAs but still higher than the average cellular mRNA. Late in the infection cycle virus mRNAs with a relative low translational efficiency are preferentially translated under standard growth conditions whereas "early" virus mRNAs which are still present and which show a higher translational resistance to hypertonic conditions are not translated. These results indicate a unique translational control operating late in the growth cycle of vaccinia virus.