THE SACCHAROMYCES-CEREVISIAE TRANSLATION INITIATION-FACTOR TIF3 AND ITS MAMMALIAN HOMOLOG, ELF-4B, HAVE RNA ANNEALING ACTIVITY

The Saccharomyces cerevisiae TIF3 gene encodes the yeast homologue of mammalian translation initiation factor eIF-4B. The have added six histidine residues to the C-terminus of Tif3 protein (Tif3-His6p) and purified the tagged protein by affinity chromatography. Tif3-His6p stimulates translation and mRNA binding to ribosomes in a Tif3-dependent in vitro system. Furthermore, it binds to single-stranded RNA and catalyses the annealing of partially complementary RNA strands in vitro. In parallel experiments, RNA annealing activity could also be demonstrated for mammalian eIF-4B. A role for Tif3/eIF-4B and RNA annealing activity in the scanning process is proposed.