title: Binding specificity of the two major DNA-binding proteins in human serum.
abstract: The two major DNA-binding proteins of human serum (DNA-binding protein 1 and DNA-binding protein 2) were shown to bind preferentially to single-stranded polynucleotides rich in guanine residues. Equilibrium competition experiments using a nitrocellulose filter assay system containing labeled human lymphocyte DNA and various competing natural and synthetic polynucleotides indicated that both proteins recognized sequences of bases containing a keto group in either position 6 (purines) or 4 (pyrimidines) and that these keto groups must be readily accessible for effective binding to occur. Guanine was shown to be the preferred nucleotide through inhibition experiments using a series of synthetic homopolymers and a series of bacterial DNAs of differing G + C content. The relationship between protein affinity and G + C content was shown to be directly proportional. The equilibrium constants for the binding of the human lymphocyte DNA by both proteins were on the order of 10(-6) M, and the length of the nucleotide sequence necessary for effective binding was found to be 12 to 18 bases using a series of oligomers of poly(dG).
mesh_terms: D002352:Carrier Proteins / Q000097:blood* / Q000302:isolation & purification; D002460:Cell Line; D004247:DNA / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008214:Lymphocytes; D013329:Structure-Activity Relationship
chemical_list: D002352:Carrier Proteins; D004247:DNA