The alpha-subunit of the mammalian guanine nucleotide-exchange factor eIF-2B is essential for catalytic activity in vitro.
Eukaryotic initiation factor (eIF)-2B, the guanine nucleotide exchange factor for eIF-2, consists of five distinct subunits in both mammals and the yeast Saccharomyces cerevisiae. The exchange reaction mediated by eIF-2B can be regulated by phosphorylation of eIF-2 on its alpha-subunit. This represents a key control point in the initiation of translation. The functions of the individual subunits of the eIF-2B complex remain unclear. Mutational analysis in Saccharomyces cerevisiae suggested that the smallest subunit (the alpha) is dispensable for exchange, but required for the inhibition of eIF-2B by eIF-2(alphaP). Here we present evidence that, in mammalian cells, eIF-2Balpha is essential for the activity of the complex, since preparations of eIF-2B lacking this subunit are not active in nucleotide exchange in vitro, although the complex still contains the beta, gamma, delta and epsilon subunits.
Craddock
B L
BL
Department of Biochemistry, School of Medical Sciences, University of Bristol, United Kingdom.
Proud
C G
CG
D000818:Animals; D015153:Blotting, Western; D002384:Catalysis; D004252:DNA Mutational Analysis; D004591:Electrophoresis, Polyacrylamide Gel; D015852:Eukaryotic Initiation Factor-2 / Q000302:isolation & purification / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D007700:Kinetics; D046911:Macromolecular Substances; D008322:Mammals; D010442:Peptide Chain Initiation, Translational; D010766:Phosphorylation; D011506:Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D012156:Reticulocytes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism
D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D046911:Macromolecular Substances; D011506:Proteins; D011994:Recombinant Proteins