title: Wheat germ poly(A) binding protein enhances the binding affinity of eukaryotic initiation factor 4F and (iso)4F for cap analogues.
abstract: Most eukaryotic mRNAs contain a 5' cap (m7GppX) and a 3' poly(A) tail to increase synergistically the translational efficiency. Recently, the poly(A) binding protein (PABP) and cap-binding protein, eIF-4F, were found to interact [Le et al. (1997) J. Biol. Chem. 272, 16247-16255; Tarun and Sachs (1996) EMBO J. 15, 7168-7177]. These data suggest that PABP may exert its effect on translational efficiency either by increasing the formation of initiation factor-mRNA complex or by enhancing ribosome recycling. To investigate the functional consequences of these interactions, the fluorescent cap analogue, ant-m7GTP, which is an environmentally sensitive fluorescent probe [Ren and Goss (1996) Nucleic Acids Res. 24, 3629-3634] was used to investigate the cap-binding affinity. Our data show that the binding of eIF-(iso)4F or eIF-4F to cap analogue enhanced their binding affinity toward PABP approximately 40-fold. Similarly, the eIF-4F/PABP or eIF-(iso)4F/PABP complexes show a 40-fold enhancement of cap analogue binding as compared to eIF-4F or eIF-(iso)4F alone. At least part of the enhancement of the translational initiation by PABP can be accounted for by direct changes in cap-binding affinity. The interactions of these components also suggest a mechanism whereby the poly(A) tail is brought into close proximity with m7G cap. This effect was examined by fluorescence energy transfer, and it was determined that the PABP/eIF-4F complex could bind both poly(A) and 5' cap simultaneously.
authors.affiliation: Department of Chemistry, Hunter College, City University of New York 10021, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Wei
authors.forename: M L
authors.initials: ML
authors.lastname: Balasta
authors.forename: J
authors.initials: J
authors.lastname: Ren
authors.forename: D J
authors.initials: DJ
authors.lastname: Goss
mesh_terms: D001665:Binding Sites / Q000187:drug effects / Q000235:genetics; D039562:Eukaryotic Initiation Factor-4F; D005454:Fluorescence Polarization; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010940:Plant Proteins / Q000502:physiology*; D011061:Poly A / Q000378:metabolism*; D039102:Poly(A)-Binding Proteins; D012314:RNA Cap Analogs / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000502:physiology*; D013050:Spectrometry, Fluorescence; D014908:Triticum
chemical_list: D039562:Eukaryotic Initiation Factor-4F; D010448:Peptide Initiation Factors; D010940:Plant Proteins; D039102:Poly(A)-Binding Proteins; D012314:RNA Cap Analogs; D016601:RNA-Binding Proteins; D011061:Poly A