Discriminatory interaction of purified eukaryotic initiation factors 4F plus 4A with the 5' ends of reovirus messenger RNAs.

The interaction of several reovirus mRNAs with cap-binding initiation factors has been investigated. Two quantitative experimental techniques have been applied to this question: (a) the rates of reaction of different mRNAs with tobacco acid pyrophosphatase and (b) the extent of cross-linking of different mRNAs to initiation factors in the presence and absence of ATP. The effects of ionic strength on these reactions have also been investigated. Our results demonstrate for the first time that the purified initiation factors interact differentially with purified reovirus mRNAs under competitive conditions and thus confirm earlier interpretations based on kinetic data. Comparison of the data from these studies with the translational behavior of the reovirus mRNAs, both in vitro and in vivo, has also led to specific predictions about features of these mRNAs that determine their competitive efficiencies. 1) Under ordinary ionic conditions, the steric accessibility of the m7G cap moiety of a reovirus mRNA appears to be a major determinant of its translation rate. 2) When the ionic strength is increased to supranormal levels, an additional feature, which may simply be the amount of secondary structure formed by sequences proximal to the cap, can become rate-limiting for several, but not all, of these mRNAs.