Eukaryotic initiation factor

http://en.wikipedia.org/wiki/Eukaryotic_initiation_factor

FIGURE 1 | Model of the canonical pathway of eukaryotic translation initiation.

Nature Reviews Molecular Cell Biology 11, 113-127 (February 2010)

Mechanism of cap-dependent translation initiation. Schematic representation of the closed-loop model of translation initiation. In this model, the eIF4F complex interacts with both the 5'end of the mRNA (via eIF4E) and the poly(A) tail (via PABP) and recruits the 40S ribosomal subunit via its interaction with eIF3. For simplicity, other proteins, as well as a second eIF4A molecule known to interact with eIF4G, have been omitted.

a | The recruitment of the 40S ribosomal subunit to the 5' end of mRNA is a crucial and rate-limiting step during cap-dependent translation. A number of translation initiation factors, including the 5' cap-binding protein eukaryotic translation initiation factor 4E (eIF4E), have essential roles in this process. Signal transduction-mediated phosphorylation events regulate the function of eIF4E. For example, hypophosphorylated 4E-binding proteins (4E-BPs) bind tightly to eIF4E, thereby preventing its interaction with eIF4G and thus inhibiting translation. Mammalian target of rapamycin complex 1 (mTORC1)-mediated phosphorylation of 4E-BPs releases the 4E-BP from eIF4E, resulting in the recruitment of eIF4G to the 5' cap, and thereby allowing translation initiation to proceed. b | Another well-studied initiation factor that is targeted by signal transduction pathways is eIF4B. Following 40S ribosomal protein S6 kinase (S6K)- or ribosomal S6 kinase (RSK)-mediated phosphorylation, eIF4B is recruited to the translation pre-initiation complex and enhances the RNA helicase activity of eIF4A. This is particularly important for translating mRNAs that contain long and structured 5' untranslated region sequences, because the unwinding of these RNA structures is required for efficient 40S ribosomal subunit scanning towards the initiation codon. GF, growth factor.

Alignment of SpolvlgA central and C-terminal region with other DDX3/PL10 genes. Conserved amino acids are indicated with boxes. Known conserved motifs are indicated with color boxes. Sequences used for the alignment indicating organism and accession number: SpolvlgA, Schmidtea polychroa, FJ599746; DjVLGA, Dugesia japonica, AB017002; HsDDX3X, Homo sapiens, NM_001356; MmDDX3X, Mus musculus, NM_010028; DrDDX3, Danio rerio, BC133162; DmBelle, Drosophila melanogaster, NM_080522; ScDBP1, Saccharomyces cerevisiae, NP_015206.

Int J Biol Sci 2009; 5(1):64-73