The effect of ethanol on polypeptide chain initiation in reticulocyte lysates. Inhibition of recycling of initiation factor eIF-2.
Using the reticulocyte cell-free system, we have investigated the mechanism by which ethanol inhibits the initiation of protein synthesis. Ethanol inhibited the formation of 40S-initiation complexes, and this effect correlated well with the inhibition by ethanol of overall peptide-chain initiation. Ethanol was a more potent inhibitor of translation at 37 degrees than at 30 degrees. The inhibition of peptide-chain initiation and 40S-initiation complex formation in reticulocyte lysates under other conditions is associated with increased phosphorylation of the alpha-subunit of protein synthesis initiation factor-2 (eIF-2 alpha) and the inhibition of recycling of this factor. Recycling of eIF-2 is mediated by another protein factor GEF (= guanine nucleotide-exchange factor). The addition of ethanol to reticulocyte lysates led to increased phosphorylation of eIF-2 alpha and to a decrease in the rate of exchange of guanine nucleotides bound to eIF-2. This second finding indicated that recycling of eIF-2 was impaired probably due to decreased availability of GEF. Using purified components it was found that ethanol inhibited the ability of GEF to stimulate eIF-2 and that this inhibition showed a similar temperature dependence to the effect of ethanol on overall protein synthesis. Taken together, these results suggest that ethanol leads to inhibition of peptide-chain initiation both through increased phosphorylation of eIF-2 alpha and by directly inhibiting the productive interaction of eIF-2 and GEF.
Cox
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Biological Laboratory, University of Kent, Canterbury, U.K.
Proud
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CG
D000431:Ethanol / Q000494:pharmacology*; D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects*; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D012156:Reticulocytes / Q000378:metabolism; D019892:eIF-2 Kinase
D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D010448:Peptide Initiation Factors; D011506:Proteins; D000431:Ethanol; D011494:Protein Kinases; D019892:eIF-2 Kinase; D008274:Magnesium