GTP HYDROLYSIS DURING METHIONYL-TRANSFER-RNA BINDING TO 40-S RIBOSOMAL-SUBUNITS AND SITE OF EDEINE INHIBITION

Abstract

Three lines of evidence are presented indicating that GTP hydrolysis associated with eukaryotic peptide initiation occurs in the absence of 60 S subunits when methionyl-tRNAf is bound to 40 S ribosomal subunits. An enzyme fraction required for binding of methionyl-tRNAf to 40 S subunits and peptide initiation, tentatively equated with eIF-(4 + 5), has GTPase activity and appears to be responsible for hydrolysis of GTP in the methionyl-tRNAf .cntdot. eIF-2 .cntdot. GTP complex. Direct analysis of the methionyl-tRNAf .cntdot. 40 S complex formed with eIF-2 and [8-3H]guanine, [.gamma.-32P]GTP reveals bound guanine but not .gamma.-phosphate. Edeine, a peptide antibiotic containing spermidine and .beta.-tyrosine residues at its COOH terminus and NH2 terminus, respectively, blocks peptide initiation and interferes with binding of methionyl-tRNAf to 40 S ribosomal subunits. Inhibition of binding is observed when the eIF-2-mediated binding reaction is carried out with GTP but not with guanosine 5''-(.beta.,.gamma.-methylene)triphosphate or guanosine 5''-(.beta.,.gamma.-imido)triphosphate. Edeine was labeled by iodination and shown to bind with high affinity to 40 S but not to 60 S ribosomal subunits. Edeine possibly blocks a specific site on the 40 S ribosomal subunit to which a segment of the methionyl-tRNAf molecule is bound during the course of the initiation reaction sequence. [Ribosomal preparations from rabbit reticulocytes and Artemia salina were used in this study.].