A PROTEIN COMPLEX OF TRANSLATIONAL REGULATORS OF GCN4 MESSENGER-RNA IS THE GUANINE NUCLEOTIDE-EXCHANGE FACTOR FOR TRANSLATION INITIATION FACTOR-II IN YEAST
Am. Cigan et al., A PROTEIN COMPLEX OF TRANSLATIONAL REGULATORS OF GCN4 MESSENGER-RNA IS THE GUANINE NUCLEOTIDE-EXCHANGE FACTOR FOR TRANSLATION INITIATION FACTOR-II IN YEAST, Proceedings of the National Academy of Sciences of the United Statesof America, 90(11), 1993, pp. 5350-5354
In Saccharomyces cerevisiae, phosphorylation of the alpha subunit of t
ranslation initiation factor 2 (eIF-2) by protein kinase GCN2 stimulat
es translation of GCN4 mRNA. In mammalian cells, phosphorylation of eI
F-2alpha inhibits the activity of eIF-2B, the GDP-GTP exchange factor
for eIF-2. We present biochemical evidence that five translational reg
ulators of GCN4 encoded by GCD1, GCD2, GCD6, GCD7, and GCN3 are compon
ents of a protein complex that stably interacts with eIF-2 and represe
nts the yeast equivalent of eIF-2B. In vitro, this complex catalyzes g
uanine nucleotide exchange on eIF-2 and overcomes the inhibitory effec
t of GDP on formation of eIEF-2.GTP.Met-initiator tRNA(Met) ternary co
mplexes. This finding suggests that mutations in GCD-encoded subunits
of the complex derepress GCN4 translation because they mimic eIF-2alph
a phosphorylation in decreasing eIF-2B activity. Our results indicate
that translational control of GCN4 involves a reduction in eIF-2B func
tion, a mechanism used in mammalian cells to regulate total protein sy
nthesis in response to stress.