Expression of vaccinia virus early mRNA in Ehrlich ascites tumor cells. 1. Translation of cellular and viral early mRNA in cell-free systems from uninfected and virus-infected cells at the early stage

Regulation of protein synthesis in virus-infected animal cells

This chapter summarizes the structural features that govern the translation of viral mRNAs: where the synthesis of a protein starts and ends, how many proteins can be produced from one mRNA, and how efficiently. It focuses on the interplay between viral and cellular mRNAs and the translational machinery. That interplay, together with the intrinsic structure of viral mRNAs, determines the patterns of translation in infected cells. It also points out some possibilities for translational regulation that can only be glimpsed at present, but are likely to come into focus in the future. The mechanism of selecting the initiation site for protein synthesis appears to follow a single formula. The translational machinery displays a certain flexibility that is exploited more frequently by viral than by cellular mRNAs. Although some of the parameters that determine efficiency have been identified, how efficiently a given mRNA will be translated cannot be predicted by summing the known parameters.

Translation of vaccinia virus and cellular mRNA in cell-free systems prepared from uninfected and vaccinia virus infected L929 cells

Cell-free translation systems were prepared from uninfected and vaccinia infected (3 and 5 hours post-infection) L929 cells. The systems were made mRNA dependent in order to translate exogenous mRNA mixtures. The overall rate of protein synthesis was similar in the three translation systems. However, one-dimensional electrophoresis showed that the systems differed in terms of the translation efficiency for individual mRNAs. This could be demonstrated with each of the following mRNA mixtures: early vaccinia mRNA synthesized by vaccinia cores in vitro, mRNA isolated from polysomes of vaccinia infected HeLa cells ("late" vaccinia mRNA) and cytoplasmic ascites mRNA. When the above mentioned groups of mRNAs were allowed to compete for translation in the cell-free systems and their products were analyzed on one-dimensional gels, the following order of translational efficiency was observed: the most prominent species of vaccinia early mRNA (other species could not be judged) were translated better than some late vaccinia mRNA species which in turn were slightly more efficiently translated than cellular mRNAs.