English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

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.

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