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Initiation factor eIF-4F: phosphorylation and interaction with other initiation factors

Journal Article · · Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States)
OSTI ID:5019808
; ;

eIF-4F, a multi-protein mRNA cap binding complex, was purified from HeLa cell S10 by m/sup 7/G-Sepharose-4B chromatography. The m/sup 7/GTP eluate was analyzed by 2-dimensional gel electrophoresis. The most abundant protein is eIF-4E (CBP-I), which exhibits two isoelectric forms. The more acidic (30%) labels with (/sup 32/P)phosphate in vivo and is lost when samples are treated with phosphatase. Analysis of heat shocked lysates reveals that eIF-4E becomes dephosphorylated, possibly accounting for the reported loss of eIF-4E activity in stressed cells. The m/sup 7/GTP eluates from normal cells also contain the other eIF-4F subunits, eIF-4A and p220, but in lower molar amounts, suggesting only part of the eIF-4E forms eIF-4F complexes. In addition, virtually all of the subunits of eIF-3 are present in amounts exceeding that of eIF-4A. eIF-4B also binds to the affinity column and elutes either with the GDP or m/sup 7/GTP washes, depending on extraction and binding conditions. The results suggest that all four initiation factors (eIF-3, eIF-4A, eIF-4B and eIF-4F) form a supermolecular complex which may be the active form of the factors for mRNA binding. Analyses of heat shocked lysates show reduced recoveries of eIF-3, eIF-4A and p220. The stability and activity of the complex correlates with the phosphorylation of the eIF-4E subunit, and thus phosphorylation may regulate the activity of eIF-4F in HeLa cells.

Research Organization:
Univ. of California School of Medicine, Davis
OSTI ID:
5019808
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
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMATOGRAPHY
DAYS LIVING RADIOISOTOPES
ELECTROPHORESIS
HELA CELLS
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGHT NUCLEI
MESSENGER-RNA
NUCLEI
NUCLEIC ACIDS
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PHOSPHORUS 32
PHOSPHORUS ISOTOPES
PHOSPHORYLATION
PROTEINS
PURIFICATION
RADIOISOTOPES
REACTION KINETICS
RNA
SEPARATION PROCESSES
TRACER TECHNIQUES