TRP(221) IS INVOLVED IN THE PROTECTIVE EFFECT OF ELONGATION-FACTOR EEF-2 ON THE RICIN ALPHA-SARCIN SITE OF THE RIBOSOME

Elongation factor eEF-2 treated by N-bromosuccinimide under conditions which oxidize 2 Trp residues (Trp343 and Trp221) is inactivated in ri bosome-dependent GTP hydrolysis and polyphenylalanine synthesis, and i nactivation correlates with the specific oxidation of Trp221 (Guillot, D., Penin, F., Di Pietro, A., Sontag, B., Lavergne, J. P., and Reboud , J. P. (1993) J. Biol. Chem. 268, 20911-20916). It is shown here that this oxidation prevents neither GTP binding to eEF-2 nor the formatio n of the ribosome-eEF-2-GPP(NH)P complex, but that oxidized eEF-2 is n o longer able to protect ribosomes against ricin inactivation. These o bservations suggest that Trp221 or an amino-acid sequence containing t his residue interacts with the 28 S rRNA loop including the GAGA seque nce, which is the target of ricin. Such a hypothesis is discussed in r elation with data on RNA recognition motifs described in different pro teins.