TY - JOUR
T1 - eIF2 independently binds two distinct eIF2b subcomplexes that catalyze and regulate guanine-nucleotide exchange
AU - Pavitt, Graham D.
AU - Ramaiah, Kolluru V.A.
AU - Kimball, Scot R.
AU - Hinnebusch, Alan G.
PY - 1998/2/15
Y1 - 1998/2/15
N2 - eIF2B is a heteropentameric guanine-nucleotide exchange factor essential for protein synthesis initiation in eukaryotes. Its activity is inhibited in response to starvation or stress by phosphorylation of the α subunit of its substrate, translation initiation factor eIF2, resulting in reduced rates of translation and cell growth. We have used an in vitro nucleotide-exchange assay to show that wild-type yeast eIF2B is inhibited by phosphorylated eIF2 [eIF2(αP)] and to characterize eIF2B regulatory mutations that render translation initiation insensitive to eIF2 phosphorylation in vivo. Unlike wild-type eIF2B, eIF2B complexes with mutated GCN3 or GCD7 subunits efficiently catalyzed GDP exchange using eIF2(αP) as a substrate. Using an affinity-binding assay, we show that an eIF2B subcomplex of the GCN3, GCD7, and GCD2 subunits binds to eIF2 and has a higher affinity for eIF2(αP), but it lacks nucleotide-exchange activity. In contrast, the GCD1 and GCD6 subunits form an eIF2B subcomplex that binds equally to eIF2 and eIF2(αP). Remarkably, this second subcomplex has higher nucleotide-exchange activity than wild-type eIF2B that is not inhibited by eIF2(αP). The identification of regulatory and catalytic eIF2B subcomplexes leads us to propose that binding of eIF2(αP) to the regulatory subcomplex prevents a productive interaction with the catalytic subcomplex, thereby inhibiting nucleotide exchange.
AB - eIF2B is a heteropentameric guanine-nucleotide exchange factor essential for protein synthesis initiation in eukaryotes. Its activity is inhibited in response to starvation or stress by phosphorylation of the α subunit of its substrate, translation initiation factor eIF2, resulting in reduced rates of translation and cell growth. We have used an in vitro nucleotide-exchange assay to show that wild-type yeast eIF2B is inhibited by phosphorylated eIF2 [eIF2(αP)] and to characterize eIF2B regulatory mutations that render translation initiation insensitive to eIF2 phosphorylation in vivo. Unlike wild-type eIF2B, eIF2B complexes with mutated GCN3 or GCD7 subunits efficiently catalyzed GDP exchange using eIF2(αP) as a substrate. Using an affinity-binding assay, we show that an eIF2B subcomplex of the GCN3, GCD7, and GCD2 subunits binds to eIF2 and has a higher affinity for eIF2(αP), but it lacks nucleotide-exchange activity. In contrast, the GCD1 and GCD6 subunits form an eIF2B subcomplex that binds equally to eIF2 and eIF2(αP). Remarkably, this second subcomplex has higher nucleotide-exchange activity than wild-type eIF2B that is not inhibited by eIF2(αP). The identification of regulatory and catalytic eIF2B subcomplexes leads us to propose that binding of eIF2(αP) to the regulatory subcomplex prevents a productive interaction with the catalytic subcomplex, thereby inhibiting nucleotide exchange.
UR - http://www.scopus.com/inward/record.url?scp=0032519585&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0032519585&partnerID=8YFLogxK
U2 - 10.1101/gad.12.4.514
DO - 10.1101/gad.12.4.514
M3 - Article
C2 - 9472020
AN - SCOPUS:0032519585
VL - 12
SP - 514
EP - 526
JO - Genes and Development
JF - Genes and Development
SN - 0890-9369
IS - 4
ER -