title: Protein synthesis in Drosophila melanogaster embryos. Two mechanisms for guanine nucleotide exchange on eukaryotic initiation factor 2.
abstract: The mechanism for guanine nucleotide exchange with eukaryotic initiation factor-2 (eIF-2) from Drosophila melanogaster embryos was studied using the reaction eIF-2 X [3H]GDP + GDP (GTP) in equilibrium eIF-2 X GDP (GTP) + [3H]GDP. When highly purified eIF-2 is used the rate of nucleotide exchange is greatly reduced by Mg2+ and this reduction is overcome by the guanine-nucleotide-exchange factor (GEF) of rabbit reticulocytes. This GEF-dependent exchange is inhibited when Drosophila eIF-2 is either phosphorylated by the hemin-controlled inhibitor (HCI) of rabbit reticulocytes or treated with phosphatidylserine or a rabbit eIF-2 X phosphatidylserine complex. The Mg2+ impairment of guanine nucleotide exchange is less severe when highly purified eIF-2 is incubated at a higher temperature (37 degrees C) and is not observed at any temperature if partially purified eIF-2 is used instead of the highly purified factor. In the latter two cases the exchange is not inhibited by either phosphorylation with HCI or phospholipid treatment of Drosophila eIF-2, possibly suggesting that the observed exchange is not mediated by a GEF-like factor. Our data support two possible mechanisms for GDP/GTP exchange with Drosophila embryos eIF-2: a GEF-dependent exchange, similar to that described in rabbit reticulocytes, which may be regulated by phosphorylation of eIF-2, and a factor-independent exchange which appears to be insensitive to this type of control.
mesh_terms: D000818:Animals; D004331:Drosophila melanogaster / Q000196:embryology / Q000378:metabolism*; D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D006150:Guanine Nucleotides / Q000378:metabolism*; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010718:Phosphatidylserines / Q000494:pharmacology; D010766:Phosphorylation; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism* / Q000502:physiology
chemical_list: D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D006150:Guanine Nucleotides; D010448:Peptide Initiation Factors; D010718:Phosphatidylserines; D011506:Proteins