Polypeptide Chain Initiation in Eukaryotes: Reversibility of the Ternary Complex-Forming Reaction.

Authors

John Siekierka, Montclair State UniversityFollow
Veeraswamy Manne, Bristol-Myers SquibbFollow
Ljubica Mauser, RocheFollow
Severo Ochoa, Universidad Autónoma de MadridFollow

Document Type

Article

Publication Date

1-1-1983

Journal / Book Title

Proceedings of the National Academy of Sciences of the United States of America (PNAS)

Abstract

In the last step of polypeptide chain initiation in eukaryotes, the interaction of the 40S preinitiation complex eIF-2.GTP.Met-tRNAi.40S [the complex between the 40S ribosomal subunit and the ternary complex containing equimolar amounts of eukaryotic initiation factor 2 (eIF-2), GTP, and eukaryotic initiator methionyl tRNA (Met-tRNAi)] with a 60S ribosomal subunit in the presence of mRNA, cap binding protein (with "capped" messengers), ATP, and the initiation factors eIF-3, eIF-4a, -4b, -4c, and eIF-5, results in the formation of an 80S initiation complex (Met-tRNAi.80S.mRNA) with concomitant hydrolysis of GTP and liberation of eIF-2 for recycling in subsequent initiation events. However, at physiological Mg2+ concentrations, GDP is known to have approximately equal to 100-fold greater affinity than GTP for eIF-2 and eIF-2 is believed to be released in the form of an eIF-2.GDP complex. Previously, we have shown that initiation factor SP (for eIF-2-stimulating protein) promotes the exchange of eIF-2-bound GDP for GTP and catalyzes ternary complex formation in the presence of Met-tRNAi. Binding of GDP by eIF-2 is indeed so tight that, as we now show, homogeneous preparations of eIF-2 contain upward of 0.5 mol of GDP/mol of eIF-2. We further show that, in the presence of Mg2+ and catalytic amounts of SP, ternary complex formation conforms to the overall reversible reaction eIF-2.GDP + GTP + Met-tRNAi in equilibrium eIF-2.GTP.Met-tRNAi + GDP.

Comments

Copyright 1983, National Academy of Sciences

DOI

10.1073/pnas.80.5.1232

Montclair State University Digital Commons Citation

Siekierka, John; Manne, Veeraswamy; Mauser, Ljubica; and Ochoa, Severo, "Polypeptide Chain Initiation in Eukaryotes: Reversibility of the Ternary Complex-Forming Reaction." (1983). Department of Chemistry and Biochemistry Faculty Scholarship and Creative Works. 150.
https://digitalcommons.montclair.edu/chem-biochem-facpubs/150