title: Salt-dependent binding of Escherichia coli initiation factor 3 to nucleic acids determined by sedimentation partition chromatography.
abstract: The binding of 14CH3- initiation factor 3 (IF3) to polynucleotides is strongly dependent upon the concentration of added salt. The observed association constant, Kobs, increases by ca. a factor of 10(2) when the NaCl concentration is lowered from 200 to 100 mM for the binding of 14CH3-IF3 to all nucleic acids examined. This salt-dependent binding suggests that at physiological salt concentrations the formation of an IF3-polynucleotide complex is primarily driven by the release of cations from the nucleic acid, although anion effects are involved also. For single-stranded nucleic acids, nonelectrostatic interactions may contribute a factor of 10(2) to the value of Kobs, although accurate assessment of these interactions is complicated by anion effects. The binding of 14CH3-IF3 to the double helix, poly(A).poly(U), appears to be exclusively electrostatic. 14CH3-IF3 forms a maximum of 8 +/- 2 ion pairs with most single-stranded polynucleotides. The value of Kobs increases from ca. 10(3) to 10(5) M-1 when the NaCl concentration is lowered from 200 to 100 mM for the binding of 14CH3-IF3 to poly(A), poly(C), poly(U), and poly(A).poly(U). At physiological salt concentrations, IF3 shows no preference for any of these bases or for single or double-stranded structures. However, 14CH3-IF3 binds ca. 60 times greater to poly(A,G), at al NaCl concentrations examined, than to the other nucleic acids, indicating that IF3 has some preference for guanine-containing polynucleotides. The presence of 10 mM Mg2+ tends to reduce the value of Kobs at any given NaCl concentration, but to a smaller degree than predicted by simply a competition between Mg2+ and IF3 for the nucleic acid lattice.
mesh_terms: D002845:Chromatography / Q000379:methods; D004926:Escherichia coli / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000378:metabolism*; D011061:Poly A / Q000378:metabolism; D011066:Poly C / Q000378:metabolism; D011072:Poly U / Q000378:metabolism; D011119:Polynucleotides / Q000378:metabolism*; D039665:Prokaryotic Initiation Factor-3; D011485:Protein Binding; D012965:Sodium Chloride / Q000494:pharmacology*
chemical_list: D010448:Peptide Initiation Factors; D011119:Polynucleotides; D039665:Prokaryotic Initiation Factor-3; D011061:Poly A; D011072:Poly U; D011066:Poly C; D012965:Sodium Chloride; D008274:Magnesium