The N terminus of eukaryotic translation elongation factor 3 interacts with 18 S rRNA and 80 S ribosomes

Elongation factor-3 (EF-3) is an essential fungal-specific translation factor which exhibits a strong ribosome-dependent ATPase activity and has sequence homologies that may predict domains critical for its role in protein synthesis, including a domain at the N terminus, which exhibits sequence homology with Escherichia coli ribosomal protein S5. A portion of the N terminus of Saccharomyces cerevisiae EF-3 (spanning the S5 homology region) has been cloned, expressed, and purified from E. coli, UV cross-linking experiments revealed that the N-terminal EF-3 protein (N-term EF-3) can be specifically cross-linked to 18 S rRNA. Filter-binding assays confirmed these data, and also established that the interaction has a K-d, similar to 238 nM. Additional evidence shows that N-term EF-3 is able to associate with yeast ribosomes and inhibit the ribosome-dependent ATPase activity of native EF-3. These data taken together suggest that at least one of the ribosome-binding sites of EF-3 is located at the N terminus.