AN INTERACTION OF WHEAT-GERM INITIATION-FACTOR 4B WITH OLIGORIBONUCLEOTIDES

The binding of oligoribonucleotides to wheat germ protein synthesis in itiation factor eIF-4B was measured by direct fluorescence techniques. An analysis of the equilibrium association constants (K-eq) indicates that eIF-4B binding is not affected by the m(7)GTP cap structure or t he AUG. eIF-4B is insensitive to hairpin structures within the oligori bonucleotide. The binding site size is approximately 18 bases. The bin ding of oligoribonucleotide to eIF-4B as a function of pH, temperature , and ionic strength is also described. The pH dependent binding showe d an increase in binding with increasing pH in contrast to the sharp p H optimum observed for cap binding protein eIF-4E (Carberry, S. E., Da rzynkiewicz, E., and Goss, D. J. (1991) Biochemistry 30, 1624-1627). A ssuming all tryptophan residues contribute to the observed fluorescenc e, iodide quenching showed that 8(+/- 1) out 9 of eIF-4B's tryptophan residues are on the surface of the eIF-4B protein. A specific anion ef fect of Cl- on eIF-4B binding to oligoribonucleotide was found when co mparing the ionic strength effect of KC2H3O2 and KCl.