Mechanism of polypeptide chain initiation in eukaryotes and its control by phosphorylation of the alpha subunit of initiation factor 2.

Proceedings of the National Academy of Sciences of the United States of America ·Vol. 79 ·No. 8 ·1982-04-00 ·Pages 2537-40

Siekierka J, Mauser L, Ochoa S

Abstract

Earlier, we isolated eukaryotic initiation factor 2 (eIF-2)-stimulating protein (SP) as a homogeneous complex with eIF-2 (eIF-2-SP) and showed that, in the presence of Mg2+, eIF-2-SP promotes formation of a ternary complex with GTP and eukaryotic initiator methionyl tRNA (Met-tRNAi) (eIF-2-GTP-Met-tRNAi) catalytically. We now show that SP-bound eIF-2 exchanges with eIF-2 (eIF-2 exchange). Furthermore, in the presence of Mg2+, eIF-2-SP catalyzes the exchange of eIF-2-bound [3H]GDP with unlabeled GDP or GTP (GDP exchange) and the release of [3H]GDP when the ternary complex is formed from eIF-2-[3H]GDP, GTP, and [35S]Met-tRNAi. All these reactions are blocked by alpha-subunit, but not by beta-subunit, phosphorylation of eIF-2. The eIF-2 and GDP exchanges are compatible with the reaction eIF-2-GDP + SP in equilibrium EIF-2-SP + GDP reminiscent of the exchange between the Tu and Ts components of prokaryotic elongation factor 1 (EF-Tu and EF-Ts, respectively) EF-Tu-GDP + EF-Ts in equilibrium EF-Tu-EF-Ts + GDP. Due to the high affinity of GDP (approximately 100 times greater than that of GDP) for eIF-2, 40S (eIF-2-GTP-Met-tRNAi-40S) to 80S (Met-tRNAi-mRNA-80S) initiation complex conversion, which is accompanied by GTP hydrolysis, probably releases eIF-2 as eIF-2-GDP. Our results suggest that, in the presence of Mg2+, GDP binding restricts the availability of eIF-2 for chain initiation and that SP relieves this restriction in a catalytic fashion, provided that the alpha subunit of eIF-2 is not phosphorylated.

MeSH Terms

Animals Eukaryotic Initiation Factor-2 Guanosine Diphosphate/metabolism Guanosine Triphosphate/metabolism Kinetics Macromolecular Substances Peptide Chain Initiation, Translational Peptide Initiation Factors/metabolism Phosphorylation Proteins/metabolism RNA, Transfer, Amino Acyl/metabolism Rabbits Reticulocytes/metabolism

Chemicals

Eukaryotic Initiation Factor-2 Macromolecular Substances Peptide Initiation Factors Proteins RNA, Transfer, Amino Acyl tRNA(m)(Met), methionine- Guanosine Diphosphate Guanosine Triphosphate

Authors & Affiliations

3 authors, click to expand affiliations / ORCID

Siekierka J

Mauser L

Ochoa S

References (18)

18 references, click to expand

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Article Info

Journal

Proceedings of the National Academy of Sciences of the United States of America

Abbr.

Proc Natl Acad Sci U S A

ISSN

0027-8424

DOI

10.1073/pnas.79.8.2537

Published

1982-04-00

Pages

2537-40

Language

English

Region

United States

NLM ID

7505876

PMCID

PMC346234

Subset

External Links

PubMed source DOI: 10.1073/pnas.79.8.2537 PMC Full Text View journal details

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Mechanism of polypeptide chain initiation in eukaryotes and its control by phosphorylation of the alpha subunit of initiation factor 2.

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