Initiation factors that bind mRNA. A comparison of mammalian factors with wheat germ factors.
Three mammalian eukaryotic initiation factors (eIF) are required for the ATP-dependent binding of mRNA to the 40 S ribosomal subunit. These three factors, eIF-4A, eIF-4B, and eIF-4F, have also been isolated from wheat germ. Three assays were used to measure the ability of the wheat germ factors to interact with and/or substitute for the mammalian factors. Two assay systems were used to measure partial reactions involving the interaction of the three factors, ATP, and mRNA: 1) RNA-dependent ATP hydrolysis and 2) cross-linking of the factors to the 5' cap of oxidized mRNA. A third assay system was used to measure the ability of the factors to support initiation of protein synthesis. The results of the ATP hydrolysis and cross-linking experiments indicate that the wheat germ factors can interact with or substitute for the mammalian factors. Wheat germ eIF-4A appears to be functionally equivalent to mammalian eIF-4A. Wheat germ eIF-4B and eIF-4F appear to be isozymes possessing functions similar to mammalian eIF-4F. Wheat germ eIF-4B does not appear to be a functional equivalent to the mammalian eIF-4B. In a complete translation system from wheat germ, mammalian factors partially substitute for wheat germ factors, whereas the wheat germ factors are ineffective in the mammalian system.
Abramson
R D
RD
Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106.
Browning
K S
KS
Dever
T E
TE
Lawson
T G
TG
Thach
R E
RE
Ravel
J M
JM
Merrick
W C
WC
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D039601:Eukaryotic Initiation Factor-4A; D039562:Eukaryotic Initiation Factor-4F; D039642:Eukaryotic Initiation Factors; D006868:Hydrolysis; D010448:Peptide Initiation Factors / Q000378:metabolism*; D011072:Poly U / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D011817:Rabbits; D014908:Triticum / Q000032:analysis*
D039562:Eukaryotic Initiation Factor-4F; D039642:Eukaryotic Initiation Factors; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; C031799:eIF-4B; D011072:Poly U; D000255:Adenosine Triphosphate; D039601:Eukaryotic Initiation Factor-4A