Biochemical evidence supporting a mechanism for cap-independent and internal initiation of eukaryotic mRNA.
The role of eukaryotic initiation factor (eIF)4B in translation is somewhat uncertain, although it appears to stimulate a variety of activities of eIF-4A and eIF-4F. Using the model RNA-dependent ATP hydrolysis assay, the ability of eIF-4B to stimulate eIF-4A and eIF-4F was investigated. The most dramatic effect of eIF-4B is to increase the affinity of eIF-4A for RNA; no effect is seen on the affinity of eIF-4A for ATP. This is not the case for eIF-4F where stimulation occurs primarily through an increase in Vmax and not a change in the affinity for RNA. The finding that eIF-4A and eIF-4B can bind to an mRNA (lacking in secondary structure), with essentially the same degree of effectiveness and affinity as would occur for natural mRNAs in the presence of eIF-4A, eIF-4B, and eIF-4F, suggests a possible role for eIF-4A and eIF-4B in both cap-independent and internal initiation.
Abramson
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RD
Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106.
Dever
T E
TE
Merrick
W C
WC
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D039601:Eukaryotic Initiation Factor-4A; D039562:Eukaryotic Initiation Factor-4F; D039642:Eukaryotic Initiation Factors; D007700:Kinetics; D010448:Peptide Initiation Factors / Q000032:analysis / Q000378:metabolism*; D011072:Poly U / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D011817:Rabbits
D039562:Eukaryotic Initiation Factor-4F; D039642:Eukaryotic Initiation Factors; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; C031799:eIF-4B; D011072:Poly U; D039601:Eukaryotic Initiation Factor-4A; D000251:Adenosine Triphosphatases