title: A circular dichroism study of Escherichia coli Initiation Factor-1 binding to polynucleotides.
abstract: Binding of Escherichia coli Initiation Factor-1 protein to the nucleic acid lattice induces alterations in the secondary structures of a variety of purine and pyrimidine containing polynucleotides in both the single and double stranded conformations, as assessed by circular dichroism spectroscopy. The helical hairpin form of poly(U), the single-stranded stacked form of poly(C), and the duplex poly(A) x poly(U) (in the presence of Mg2+) are stoichiometrically converted by Initiation Factor-1 (IF-1) to structures spectrally indistinguishable from their partially or completely thermally denatured forms. By contrast, the binding of IF-1 to double stranded poly(C), single- and double-stranded poly(A) elicited spectral responses which were interpreted in terms of diminished base-base interaction, not equivalent to that induced by thermal means. Stoichiometric endpoints of 3-5 nucleotide residues/IF-1 were determined for polynucleotide structures in those cases where light scattering artifacts at low nucleotide residue to protein ratios were absent. In the absence of Mg2+ IF-1 was unable to elicit a conformation alteration effect in poly(A) x poly(U), while for poly(U) much less of an effect was observed than in the presence of this divalent ion. The functional significance of these results is briefly considered.
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D002942:Circular Dichroism; D004926:Escherichia coli; D008274:Magnesium / Q000494:pharmacology; D010448:Peptide Initiation Factors / Q000378:metabolism*; D011063:Poly A-U / Q000032:analysis; D011066:Poly C / Q000032:analysis; D011072:Poly U / Q000032:analysis; D011119:Polynucleotides / Q000032:analysis*; D011485:Protein Binding
chemical_list: D001426:Bacterial Proteins; D010448:Peptide Initiation Factors; D011119:Polynucleotides; D011063:Poly A-U; D011072:Poly U; D011066:Poly C; D008274:Magnesium