Two forms of purified m7G-cap binding protein with different effects on capped mRNA translation in extracts of uninfected and poliovirus-infected HeLa cells.

Eukaryotic mRNA cap binding proteins were purified from ribosomal salt wash in the presence of protease inhibitors by sucrose gradient sedimentation and m7GDP-Sepharose affinity chromatography. Rabbit reticulocyte and erythrocyte proteins with sedimentation constants of less than 6 S yielded a approximately 24,000-dalton cap binding protein. It stimulated capped mRNA translation in extracts of uninfected HeLa cells but did not restore capped mRNA function in extracts prepared from poliovirus-infected cells. Restoring and stimulatory activities both were associated with a larger, approximately 8-10 S complex that included the approximately 24,000-dalton polypeptide and several higher molecular mass components. The same two translational activities were also obtained in a slightly smaller approximately 5-7 S complex from uninfected HeLa cells but were absent from poliovirus-infected cell preparations.