Formation of a translational inhibitor by interaction of phospholipid with the eukaryotic initiation factor 2.
The polypeptide chain initiation factor 2 (eIF-2) binds phospholipid (PL) and becomes a potent inhibitor of translation in hemin-supplemented reticulocyte lysates. This binding is markedly reduced by prior treatment of eIF-2 with N-ethylmaleimide. Although PL is probably bound by all three eIF-2 subunits, our results suggest that the inhibitory molecule is produced by binding to the alpha subunit because, functionally, PL binding has the same effect on eIF-2 as alpha-subunit phosphorylation. This is suggested by the following findings. (i) Like translational inhibition due to heme deficiency, inhibition by small amounts of the eIF-2 X PL complex is prevented by small amounts of the GDP exchange factor (GEF). (ii) In the presence of Mg2+, the GEF-catalyzed formation of a ternary complex (eIF-2 X GTP X Met-tRNAi in which Met-tRNAi is the eukaryotic initiator methionyl tRNA) is inhibited by eIF-2 X PL just as well as by eIF-2 alpha-subunit phosphorylation. (iii) Also in the presence of Mg2+, GEF is unable to catalyze the exchange of free GDP with eIF-2 X PL-bound GDP, as it fails to catalyze the exchange of free GDP with GDP that is bound to alpha-subunit-phosphorylated eIF-2. These observations suggest that, like alpha-subunit-phosphorylated eIF-2, eIF-2 X PL traps GEF in a nondissociable eIF-2 X PL X GEF complex, whereby GEF is no longer able to catalyze ternary complex formation and initiation is inhibited.
de Haro
C
C
de Herreros
A G
AG
Ochoa
S
S
D000818:Animals; D015852:Eukaryotic Initiation Factor-2; D006153:Guanosine Diphosphate / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000378:metabolism* / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism*; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000187:drug effects*; D011506:Proteins / Q000378:metabolism* / Q000494:pharmacology; D011817:Rabbits; D014316:Tritium
D015852:Eukaryotic Initiation Factor-2; D010448:Peptide Initiation Factors; D010743:Phospholipids; D011506:Proteins; D014316:Tritium; D006153:Guanosine Diphosphate