Modulation of the helicase activity of eIF4A by eIF4B, eIF4H, and eIF4F.
Eukaryotic initiation factor (eIF) 4A is a DEAD box RNA helicase that works in conjunction with eIF4B, eIF4H, or as a subunit of eIF4F to unwind secondary structure in the 5'-untranslated region of mRNA, which facilitates binding of the mRNA to the 40 S ribosomal subunit. This study demonstrates how the helicase activity of eIF4A is modulated by eIF4B, eIF4H, or as a subunit of eIF4F. Results indicate that a linear relationship exists between the initial rate or amplitude of unwinding and duplex stability for all factor combinations tested. eIF4F, like eIF4A, behaves as a non-processive helicase. Either eIF4B or eIF4H stimulated the initial rate and amplitude of eIF4A-dependent duplex unwinding, and the magnitude of stimulation is dependent on duplex stability. Furthermore, eIF4A (or eIF4F) becomes a slightly processive helicase in the presence of eIF4B or eIF4H. All combinations of factors tested indicate that the rate of duplex unwinding is equivalent in the 5' --> 3' and 3' --> 5' directions. However, the optimal rate of unwinding was dependent on the length of the single-stranded region of the substrate when different combinations of factors were used. The combinations of eIF4A, eIF4A + eIF4B, eIF4A + eIF4H, and eIF4F showed differences in their ability to unwind chemically modified duplexes. A simple model of how eIF4B or eIF4H affects the duplex unwinding mechanism of eIF4A is proposed.
Rogers
G W
GW
Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4935, USA.
Richter
N J
NJ
Lima
W F
WF
Merrick
W C
WC
D004247:DNA / Q000737:chemistry; D039601:Eukaryotic Initiation Factor-4A; D039562:Eukaryotic Initiation Factor-4F; D039642:Eukaryotic Initiation Factors; D010448:Peptide Initiation Factors / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D012313:RNA / Q000737:chemistry; D020365:RNA Helicases / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000502:physiology*
C111495:EIF4H protein, human; D039562:Eukaryotic Initiation Factor-4F; D039642:Eukaryotic Initiation Factors; D010448:Peptide Initiation Factors; D016601:RNA-Binding Proteins; C031799:eIF-4B; D012313:RNA; D004247:DNA; D039601:Eukaryotic Initiation Factor-4A; D020365:RNA Helicases