Since eEF1Bc is known to bind to A-rich single-stranded sequences [32] , we mutagenized the tetraloop (GAAA) sequence to either CUUG or GUUU tetraloop sequences ( Figure 3B ) that are expected to maintain the stability of the double-stranded stem. EMSA analysis showed that neither RNAs with the new tetraloop sequences bound efficiently to eEF1Bc ( Figure 3B , lanes 5-7 and 11-13). Based on the EMSA data, we conclude that the GAAA tetraloop region of SL1 is an efficient binding site for eEF1Bc in vitro. However, we cannot exclude that eEF1Bc binding may be dependent on stabilizing effects of the GNRA tetraloop on the stem structure. The loop nucleotides may or may not be involved in protein-RNA contacts.