TY - JOUR
T1 - Polypeptide chain initiation in eukaryotes
T2 - reversibility of the ternary complex-forming reaction.
AU - Siekierka, J.
AU - Manne, V.
AU - Mauser, L.
AU - Ochoa, S.
PY - 1983/3
Y1 - 1983/3
N2 - In the last step of polypeptide chain initiation in eukaryotes, the interaction of the 40S preinitiation complex eIF-2.GTP.Met-tRNAi.40S [the complex between the 40S ribosomal subunit and the ternary complex containing equimolar amounts of eukaryotic initiation factor 2 (eIF-2), GTP, and eukaryotic initiator methionyl tRNA (Met-tRNAi)] with a 60S ribosomal subunit in the presence of mRNA, cap binding protein (with "capped" messengers), ATP, and the initiation factors eIF-3, eIF-4a, -4b, -4c, and eIF-5, results in the formation of an 80S initiation complex (Met-tRNAi.80S.mRNA) with concomitant hydrolysis of GTP and liberation of eIF-2 for recycling in subsequent initiation events. However, at physiological Mg2+ concentrations, GDP is known to have approximately equal to 100-fold greater affinity than GTP for eIF-2 and eIF-2 is believed to be released in the form of an eIF-2.GDP complex. Previously, we have shown that initiation factor SP (for eIF-2-stimulating protein) promotes the exchange of eIF-2-bound GDP for GTP and catalyzes ternary complex formation in the presence of Met-tRNAi. Binding of GDP by eIF-2 is indeed so tight that, as we now show, homogeneous preparations of eIF-2 contain upward of 0.5 mol of GDP/mol of eIF-2. We further show that, in the presence of Mg2+ and catalytic amounts of SP, ternary complex formation conforms to the overall reversible reaction eIF-2.GDP + GTP + Met-tRNAi in equilibrium eIF-2.GTP.Met-tRNAi + GDP.
AB - In the last step of polypeptide chain initiation in eukaryotes, the interaction of the 40S preinitiation complex eIF-2.GTP.Met-tRNAi.40S [the complex between the 40S ribosomal subunit and the ternary complex containing equimolar amounts of eukaryotic initiation factor 2 (eIF-2), GTP, and eukaryotic initiator methionyl tRNA (Met-tRNAi)] with a 60S ribosomal subunit in the presence of mRNA, cap binding protein (with "capped" messengers), ATP, and the initiation factors eIF-3, eIF-4a, -4b, -4c, and eIF-5, results in the formation of an 80S initiation complex (Met-tRNAi.80S.mRNA) with concomitant hydrolysis of GTP and liberation of eIF-2 for recycling in subsequent initiation events. However, at physiological Mg2+ concentrations, GDP is known to have approximately equal to 100-fold greater affinity than GTP for eIF-2 and eIF-2 is believed to be released in the form of an eIF-2.GDP complex. Previously, we have shown that initiation factor SP (for eIF-2-stimulating protein) promotes the exchange of eIF-2-bound GDP for GTP and catalyzes ternary complex formation in the presence of Met-tRNAi. Binding of GDP by eIF-2 is indeed so tight that, as we now show, homogeneous preparations of eIF-2 contain upward of 0.5 mol of GDP/mol of eIF-2. We further show that, in the presence of Mg2+ and catalytic amounts of SP, ternary complex formation conforms to the overall reversible reaction eIF-2.GDP + GTP + Met-tRNAi in equilibrium eIF-2.GTP.Met-tRNAi + GDP.
UR - http://www.scopus.com/inward/record.url?scp=0020726936&partnerID=8YFLogxK
U2 - 10.1073/pnas.80.5.1232
DO - 10.1073/pnas.80.5.1232
M3 - Article
C2 - 6572381
AN - SCOPUS:0020726936
SN - 0027-8424
VL - 80
SP - 1232
EP - 1235
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 5
ER -