J. Biol. Chem., Vol. 261, Issue 17, 7723-7728, Jun, 1986
Identification of ribosome-bound eukaryotic initiation factor 2.GDP binary complex as an intermediate in polypeptide chain initiation reaction
P Raychaudhuri and U Maitra
Studies on the formation and release of the eukaryotic initiation factor
(eIF)-2.GDP binary complex formed during eIF-5-mediated assembly of an 80 S
initiation complex have been carried out. Incubation of a 40 S initiation
complex with eIF-5, in the presence or absence of 60 S ribosomal subunits
at 25 degrees C, causes rapid and quantitative hydrolysis of ribosome-bound
GTP to form an eIF-2.GDP binary complex and Pi. Analysis of both reaction
products by Sephadex G-200 gel filtration reveals that while Pi is released
from ribosomes, the eIF- 2.GDP complex remains bound to the ribosomal
initiation complex. The eIF-2.GDP binary complex can however be released
from ribosome by subjecting the eIF-5-catalyzed reaction products to either
longer periods of incubation at 37 degrees C or sucrose gradient
centrifugation. Furthermore, addition of a high molar excess of isolated
eIF-2.GDP binary complex to a 40 S initiation reaction mixture does not
cause exchange of ribosome-bound eIF-2.GDP complex formed by
eIF-5-catalyzed hydrolysis of GTP. These results indicate that eIF- 2.GDP
complex is directly formed on the surface of ribosomes following hydrolysis
of GTP bound to a 40 S initiation complex, and that ribosome- bound eIF-2 X
GDP complex is an intermediate in polypeptide chain initiation reaction.