Conformational Control of the Interaction of Eukaryotic Elongation Factors EF-1 and EF-2 with Ribosomes

Abstract

As in the case with prokaryotic systems,

A molecular clamp ensures allosteric coordination of peptidyltransfer and ligand binding to the ribosomal A-site

“…compare G2912, C2929, U2953, G2977, C2985, A2995, G3003, A3006, G3009, U3019, U3023 and A3033 between the K237A and R247A mutants in Figure 4 A) is consistent with the idea that they also have opposing effects on PTC conformation and functionality. In addition, early studies demonstrated that while empty ribosomes are heterogeneous in their affinity for eEF2, consisting of two sub-populations having K d ’s for eEF2 ranging from subnanomolar to hundreds of nanomoles ( 60 ), the affinity for eEF2 strongly depends on the functional status of the ribosome as determined by the occupancy status of the A- and P-sites ( 61 , 62 ). This suggests that the R247A and the double mutants that increased eEF2 affinity shift this equilibrium as well, possibly stabilizing ribosomes in the pre-translocation state, and that the interactions between the 25S rRNA bases and L3 amino acid residues investigated here are involved in transitions between the pre- and post-translocational states.…”

Relationship between elongation factor 1- and elongation factor 2-dependent guanosine triphosphatase activities of ribosomes. Inhibition of both activities by ricin

“…It has been suggested that the two eukaryotic elongation factors EF1 and EF2 bind either to a unique site on the ribosome or to closely overlapping sites, the presence of each factor excluding the interaction ofthe other (Richter, 1973;Nombela & Ochoa, 1973). If the site were unique, a toxic substance which damages it should interfere with the correct interaction of both elongation factors.…”

“…Recent experiments (Richter, 1973;Nombela & Ochoa, 1973) indicate that EF1 and EF2 interact in a mutually exclusive fashion with 80S ribosomes, suggesting that both factors compete for a common binding region on the ribosome. It is still open to discussion whether the interaction of the two factors with ribosomes occurs at the same site or whether it * Abbreviations: designation of the elongation factors of eukaryotic origin as EFI and EF2 and of the respective prokaryotic factors as EF T (EF Tu and EF Ts) and EFG conforms to currently accepted nomenclature (Caskey et al, 1972); A site, aminoacyl-tRNA site; P site, peptidyl-tRNA site; GTPase, guanosine triphosphatase; GMP-P(CH2)P, guanosine (#,y-methylene) triphosphate.…”

Hydrolysis of GTP on elongation factor Tu.ribosome complexes promoted by 2'(3')-O-L-phenylalanyladenosine.

“…Interestingly, the fact that Phe-tRNAPhe or AcPhe-tRNAPhe bound to the A site does not inhibit the AdoPhe-promoted GTPase indicates that the EF-Tu-binding site on the ribosome can bind the factor not only when the nearby A site is vacant, but also when it is occupied by aminoacyl-tRNA or peptidyl-tRNA. Consequently, the control that during the elongation cycle restricts the binding of the aminoacyl-tRNA-EF-Tu-GTP complex to only those ribosomes with vacant A site (posttranslocated ribosomes) (34,35) …”