The conversion of eIF-2.GDP to eIF-2.GTP by eIF-2B requires Met-tRNA(fMet).
We have investigated why the recycling of eIF-2.GDP to eIF-2.GTP, mediated by the guanine nucleotide exchange factor eIF-2B, is rapid in rabbit reticulocyte lysate, reconstituted for optimal protein synthesis, but slow in an isolated reaction with purified eIF-2B. We have found that purified eIF-2B dissociates eIF-2.[3H]GDP as efficiently in the presence of GTP as it does in the presence of GDP provided Met-tRNA(fMet) is added. tRNA(fMet) is ineffective, and there is no Met-tRNA(fMet) requirement for exchange with GDP. Exchange of eIF-2 bound GDP for GTP is completely dependent upon Met-tRNA(fMet) in the presence of ATP, suggesting that under physiological conditions efficient recycling of eIF-2.GDP to eIF-2.GTP requires conversion of the latter, a relatively unstable complex, to a more stable Met-tRNA(fMet).eIF-2.GTP complex.
Gross
M
M
Department of Pathology, University of Chicago, IL 60637.
Rubino
M S
MS
Hessefort
S M
SM
D000818:Animals; D001667:Binding, Competitive; D002474:Cell-Free System; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006165:Guanylyl Imidodiphosphate / Q000378:metabolism; D007700:Kinetics; D009711:Nucleotides / Q000378:metabolism / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D012358:RNA, Transfer, Met / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism
D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; C072113:Met-tRNA(f)(Met); D009711:Nucleotides; D011506:Proteins; D012346:RNA, Transfer, Amino Acyl; D012358:RNA, Transfer, Met; C024988:tRNA, formylmethionine-; D006153:Guanosine Diphosphate; D006165:Guanylyl Imidodiphosphate; D006160:Guanosine Triphosphate