Eukaryotic initiation factors

Initiation of protein synthesis requires that an mRNA molecule be selected for translation by a ribosome. Once the mRNA binds to the ribosome, the latter finds the correct reading frame on the mRNA, and translation begins. This process involves tRNA, rRNA, mRNA, and at least ten eukaryotic initiation factors (elFs), some of which have multiple (three to eight) subunits. Also involved are GTP, ATP, and amino acids. Initiation can be divided into four steps (1) dissociation of the ribosome into its 40S and 60S subunits (2) binding of a ternary complex consisting of met-tRNAf GTP, and eIF-2 to the 40S ribosome to form a preinitiation complex (3) binding of mRNA to the 40S preinitiation complex to form a 43S initiation complex and (4) combination of the 43S initiation complex with the 60S ribosomal subunit to form the SOS initiation complex. 

Previously, it has been reported that the amounts of eukaryotic initiation factors in wheat germ extract prepared by a common method were deficient for the translation of some kinds of mRNAs including a-amylase mRNA and (i-globin mRNA [2]. Therefore, it can be expected that the activity of wheat germ extract prepared by a common method can be enhanced by the simple addition of extract containing deficient initiation factors. In this study, a wheat germ extract was further purified partially by ammonium sulfate fractionation... 

The catalytic activities of the fortified wheat germ cell-free systems supplemented with each fraction were investigated (Fig. 2). As shown in Fig. 2, only 0 - 40 % ammonium sulfate fraction showed an enhancement in DHFR protein synthesis. This enhancement of protein experimental results and the fact that the various eukaryotic initiation factors are contained in synthesis was also confirmed by SDS-PAGE and autoradiography (Fig. 3). From the above 0-40 % ammonium sulfate fraction [5, 6], it can be concluded that the amount of initiation factors in a conventionally prepared wheat germ cell-fi extract is deficient for the translation of DHFR with internal ribosome entry site. Therefore, it needs to supplement a wheat germ cell-free extract with the fraction containing the limited initiation factors for the efficient protein translation, and this fortified cell-free system can be easily made by simple... 

Figure 7.5 Model of ferritin (and erythroid a-aminolaevulinate synthase) translation/ribosome binding regulation by IRP. In (a), with IRP not bound to the IRE (1) binding of the 43S preinitiation complex (consisting of the small ribosomal 40S subunit, GTP and Met-tRNAMet) to the mRNA is assisted by initiation factors associated with this complex, as well as additional eukaryotic initiation factors (elFs) that interact with the mRNA to facilitate 43S association. Subsequently (2), the 43S preinitiation complex moves along the 5 -UTR towards the AUG initiator codon, (3) GTP is hydrolysed, initiation factors are released and assembly of the 80S ribosome occurs. Protein synthesis from the open reading frame (ORF) can now proceed. In (b) With IRP bound to the IRE, access of the 43S preinitiation complex to the mRNA is sterically blocked. From Gray and Hentze, 1994, by permission of Oxford University Press.

Isolation and Identification of Eukaryotic Initiation Factor 4A as a Molecular Target for the Marine Natural Product Pateamine A 303... 

Purification of FLAG-Tagged Eukaryotic Initiation Factor 2B Complexes, Subcomplexes, and Fragments from Saccharomyces cerevisiae... 

Fabian, J. R., Kimball, S. R., Heinzinger, N. K., and Jefferson, L. S. (1997). Subunit assembly and guanine nucleotide exchange activity of eukaryotic initiation factor-2B expressed in Sf9 cells. J. Biol. Chem. 272, 12359—12365. 

Konieczny, A., and Safer, B. (1983). Purification of the eukaryotic initiation factor 2-eukaryotic initiation factor 2B complex and characterization of its guanine nucleotide exchange activity during protein synthesis initiation. J. Biol. Chem. 258, 3402—3408. 

Kyrpides, N. C., and Woese, C. R. (1998). Archaeal translation initiation revisited The initiation factor 2 and eukaryotic initiation factor 2B alpha-beta-delta subunit families. Proc. Natl. Acad. Sci. USA 95, 3726—3730. 

Li, W., Wang, X., Van Der Knaap, M. S., and Proud, C. G. (2004). Mutations linked to leukoencephalopathy with vanishing white matter impair the function of the eukaryotic initiation factor 2B complex in diverse ways. Mol. Cell Biol. 24, 3295—3306. 

Matts, R. L., Levin, D. H., and London, I. M. (1983). Effect of phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 on the function of reversing factor in the initiation of protein synthesis. Proc. Natl. Acad. Sci. USA 80, 2559—2563. 

Mohammad-Qureshi, S. S., Haddad, R., Hemingway, E. J., Richardson, J. P., and Pavitt, G. D. (2007). Critical contacts between the eukaryotic initiation factor 2B (elF2B) catalytic domain and both elF2/i and 2y mediate guanine nucleotide exchange. Mol. Cell. Biol. 27, in press. 

Panniers, R., and Henshaw, E. C. (1983). A GDP/GTP exchange factor essential for eukaryotic initiation factor 2 cycling in Ehrlich ascites tumor cells and its regulation by eukaryotic initiation factor 2 phosphorylation. J. Biol. Chem. 258, 7928—7934. 

Wang, X., Paulin, F. E., Campbell, L. E., Gomez, E., O Brien, K., Morrice, N., and Proud, C. G. (2001). Eukaryotic initiation factor 2B Identification of multiple phosphorylation sites in the epsilon-subunit and their functions in vivo. EMBO J. 20,... 

Asano, K., Clayton, J., Shalev, A., and Hinnebusch, A. G. (2000). A multifactor complex of eukaryotic initiation factors elPl, eIF2, eIF3, eIF5, and initiator tRNAMet is an important translation initiation intermediate in vivo. Genes Dev. 14, 2534—2546. 

Nielsen, K. H., Valasek, L., Sykes, C., Jivotovskaya, A., and Hinnebusch, A. G. (2006). Interaction of the RNP1 motif in PRT1 with HCR1 promotes 40S binding of eukaryotic initiation factor 3 in yeast. Mol. Cell. Biol. 26, 2984—2998. 

Singh, C. R., He, H., Ii, M., Yamamoto, Y., and Asano, K. (2004). Efficient incorporation of eukaryotic initiation factor 1 into the multifactor complex is critical for formation of functional ribosomal preinitiation complexes in vivo.J. Biol. Chem. 279, 31910-31920. 

Dang, Y., Kedersha, N., Low, W. K., Romo, D., Gorospe, M., Kaufman, R., Anderson, P., and Liu, J. O. (2006). Eukaryotic initiation factor 2alpha-independent pathway of stress granule induction by the natural product pateamine A. J. Biol. Chem. 281, 32870-32878. 

Mazroui, R., Sukarieh, R., Bordeleau, M. E., Kaufman, R. J., Northcote, P., Tanaka, J., Gallouzi, I., and Pelletier, J. (2006). Inhibition of ribosome recruitment induces stress granule formation independendy of eukaryotic initiation factor 2alpha phosphorylation. Mol. Biol. Cell 17, 4212-4219. 

Borman, A. M., and Kean, K. M. (1997). Intact eukaryotic initiation factor 4G is required for hepatitis A virus internal initiation of translation. Virology 237, 129-136. 

Humphreys, D. T., Westman, B. J., Martin, D. I., andPreiss, T. (2005). MicroRNAs control translation initiation by inhibiting eukaryotic initiation factor 4E/cap and poly(A) tail function. Proc. Natl. Acad. Sci. USA 102, 16961-16966. 

Ueda, T., Watanabe-Fukunaga, R., Fukuyama, H., Nagata, S., and Fukunaga, R. (2004). Mnk2 and Mnkl are essential for constitutive and inducible phosphorylation of eukaryotic initiation factor 4E but not for cell growth or development. Mol. Cell Biol. 24, 6539-6549. 

Wang, X., Flynn, A., Waskiewicz, A. J., Webb, B. L. J., Vries, R. G., Baines, I. A., Cooper, J., and Proud, C. G. (1998). The phosphorylation of eukaryotic initiation factor eIF4E in response to phorbol esters, cell stresses, and cytokines is mediated by distinct MAP kinase pathways. J. Biol. Chem. 273, 9373-9377. 

Lazaris-Karatzas, A., Montine, K. S., and Sonenberg, N. (1990). Malignant transformation by a eukaryotic initiation factor subunit that binds to mRNA S cap. Nature 345, 544-547. 

Edery, I., Altmann, M., and Sonenberg, N. (1988). High-level synthesis in Escherichia coli of functional cap-binding eukaryotic initiation factor eIF-4E and affinity purification using a simplified cap-analog resin. Gene 74, 517-525. 

Lomakin, I. B., Hellen, C. U., and Pestova, T. V. (2000). Physical association of eukaryotic initiation factor 4G (eIF4G) with eIF4A strongly enhances binding of eIF4G to the internal ribosomal entry site of encephalomyocarditis virus and is required for internal initiation of translation. Mol. Cell Biol. 20, 6019-6029. 

Pestova, T. V., Shatsky, I. N., and Hellen, C. U. (1996b). Functional dissection of eukaryotic initiation factor 4F The 4 A subunit and the central domain of the 4G subunit are sufficient to mediate internal entry of 43S preinitiation complexes. Mol. Cell Biol. 16, 6870-6878. 

Shen, X., Tomoo, K., Uchiyama, S., Kobayashi, Y., and Ishida, T. (2001). Structural and thermodynamic behavior of eukaryotic initiation factor 4E in supramolecular formation with 4E-binding protein 1 and mRNA cap analogue, studied by spectroscopic methods. Chem. Pharm. Bull. (Tokyo) 49, 1299—1303. 

Sonenberg, N., Morgan, M. A., Merrick, W. C., and Shatkin, A. J. (1978). A polypeptide in eukaryotic initiation factors that crosslinks specifically to the 5 -terminal cap in mRNA. Proc. Natl. Acad. Sci. USA 75, 4843-4847. 

Tomoo, K., Matsushita, Y., Fujisaki, H., Abiko, F., Shen, X., Taniguchi, T., Miyagawa, H., Kitamura, K., Miura, K., and Ishida, T. (2005). Structural basis for mRNA cap-binding regulation of eukaryotic initiation factor 4E by 4E-binding protein, studied by spectroscopic, X-ray crystal structural, and molecular dynamics simulation methods. Biochim. Biophys. Acta 1753, 191—208. 

Yoder-Hill, J., Pause, A., Sonenberg, N., and Merrick, W. C. (1993). The p46 subunit of eukaryotic initiation factor (eIF)-4F exchanges with eIF-4A. J. Biol. Chem. 268, 5566-5573. 

---