Phosphorylation of mammalian initiation factor eIF-4B
The phosphorylation of initiation factors appears to be an important mechanism for regulating the rate of translation in mammalian cells. eIF-4B (80 kDa) purified from HeLa cells exhibits a complex array of 8 to 12 spots when analyzed by 2-dimensional isoelectric focusing - SDS polyacrylamide gel electrophoresis. A similar array of eIF-4B spots is seen when total lysate proteins are analyzed by immunoblotting with anti-eIF-4B antiserum or with antibodies affinity-purified from the most basic eIF-4B spot. The multiple forms of eIF-4B are due to phosphorylation, since all but the most basic spot are labeled with (/sup 32/P)phosphate in vivo and the action of alkaline phosphatase in vitro reduces the array to only two spots. Tryptic peptide maps of phosphopeptides from each of the various isoelectric variants of eIF-4B show a similar complexity, suggesting that a number of different sites are phosphorylated in a random order. When serum-deprived HeLa cells are treated with phorbol ester, both the protein synthesis rate and the extent of eIF-4B phosphorylation increase, suggesting that C kinase may be a regulator of translation. Purified C kinase phosphorylates a number of pure initiation factors in vitro, but eIF-4B is the strongest target protein. When pure eIF-4B is treated, the entire mass of eIF-4B is shifted to the most acidic spots, indicating very strong phosphorylation. Attempts are being made to detect differences in the in vitro activities of the non-phosphorylated and highly phosphorylated forms.
- Research Organization:
- Univ. of California, Davis
- OSTI ID:
- 6065716
- Report Number(s):
- CONF-870644-; TRN: 87-037627
- Journal Information:
- Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Vol. 46:6; Conference: 78. annual meeting of the American Society of Biological Chemists conference, Philadelphia, PA, USA, 7 Jun 1987
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
PHORBOL ESTERS
BIOLOGICAL EFFECTS
PHOSPHOTRANSFERASES
ENZYME ACTIVITY
PROTEINS
PHOSPHORYLATION
ALKALINE PHOSPHATASE
ELECTROPHORESIS
GENETIC MAPPING
HELA CELLS
PHOSPHATES
PHOSPHORUS 32
TRACER TECHNIQUES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARCINOGENS
CHEMICAL REACTIONS
DAYS LIVING RADIOISOTOPES
ENZYMES
ESTERASES
ESTERS
HYDROLASES
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
MAPPING
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PHOSPHATASES
PHOSPHORUS COMPOUNDS
PHOSPHORUS ISOTOPES
PHOSPHORUS-GROUP TRANSFERASES
RADIOISOTOPES
TRANSFERASES
560300* - Chemicals Metabolism & Toxicology
550201 - Biochemistry- Tracer Techniques