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Additional evidence that phosphorylation of eIF-2. cap alpha. prevents the RF-mediated dissociation of eIF-2 x GDP from the 60 S subunit of 80 S initiation complexes

Journal Article · · Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States)
OSTI ID:5019798
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The authors have recently found that eIF-2 and GTP or GDP normally bind to 60 S ribosomal subunits in rabbit reticulocyte lysate and turn over rapidly. When eIF-2..cap alpha.. is phosphorylated and polypeptide chain initiation is inhibited, eIF-2 x GDP accumulates on 60 S subunits (both free and part of an 80 S complex) due to impaired dissociation that is normally mediated by a separate protein termed RF. Using immunoblot analysis, the authors have found that phosphorylation of eIF-2..cap alpha.. causes an accumulation of RF on 80 S ribosomes as well as increased binding of eIF-2(..beta..) to 60 S and 80 S particles, decreased binding of eIF-2(..beta..) to 40 S subunits and a decrease in unbound eIF-2(..beta..). Adding (..cap alpha..-/sup 32/P)GTP to lysate with phosphorylated eIF-2..cap alpha.. gives a progressive increase in the ratio of GDP/GTP bound to 60 S and 80 S particles as the label equilibrates, suggesting that binding is by GTP with hydrolysis to GDP in 80 S complexes. Analysis of the radioactivity bound to mono and polyribosomes in lysate labeled with (/sup 35/S)Met-tRNA/sub f/ indicates a much greater ratio of Met-tRNA/sub f/ to Met-peptidyl-tRNA when eIF-2..cap alpha.. is phosphorylated. These results suggest that RF must normally promote dissociation of eIF-2 x GDP from 60 S subunit of 80 S initiation complexes before they can elongate, but cannot when eIF-2..cap alpha.. is phosphorylated, resulting in the accumulation of these complexes, some of which dissociate into 48 S complexes and 60 S x eIF-2 x GDP.

Research Organization:
Univ. of Chicago, IL
OSTI ID:
5019798
Report Number(s):
CONF-8606151-
Journal Information:
Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Journal Name: Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States) Vol. 45:6; ISSN FEPRA
Country of Publication:
United States
Language:
English

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Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
CELL CONSTITUENTS
CHEMICAL REACTIONS
DAYS LIVING RADIOISOTOPES
EVEN-ODD NUCLEI
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGHT NUCLEI
MAMMALS
NUCLEI
NUCLEIC ACIDS
NUCLEOTIDES
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANOIDS
PHOSPHORUS 32
PHOSPHORUS ISOTOPES
PHOSPHORYLATION
PROTEINS
RABBITS
RADIOISOTOPES
REACTION KINETICS
RIBOSOMES
RNA
SULFUR 35
SULFUR ISOTOPES
TRACER TECHNIQUES
TRANSFER RNA
VERTEBRATES