title: Sequence-specific binding protein of single-stranded and unimolecular quadruplex telomeric DNA from rat hepatocytes.
abstract: A rat liver nuclear protein, unimolecular quadruplex telomere-binding protein 25, (uqTBP25) is described that binds tightly and specifically single-stranded and unimolecular tetraplex forms of the vertebrate telomeric DNA sequence 5'-d(TTAGGG)n-3'. A near homogeneous uqTBP25 was purified by ammonium sulfate precipitation, chromatographic separation from other DNA binding proteins, and three steps of column chromatography. SDS-polyacrylamide gel electrophoresis and Superdex copyright 200 gel filtration disclosed for uqTBP25 subunit and native Mr values of 25.4 +/- 0.5 and 25.0 kDa, respectively. Sequences of uqTBP25 tryptic peptides were closely homologous, but not identical, to heterogeneous nuclear ribonucleoprotein A1, heterogeneous nuclear ribonucleoprotein A2/B1, and single-stranded DNA-binding proteins UP1 and HDP-1. Complexes of uqTBP25 with single-stranded or unimolecular quadruplex 5'-d(TTAGGG)4-3', respectively, had dissociation constants, Kd, of 2.2 or 13.4 nM. Relative to d(TTAGGG)4, complexes with 5'-r(UUAGGG)4-3', blunt-ended duplex telomeric DNA, or quadruplex telomeric DNA had >10 to >250-fold higher Kd values. Single base alterations within the d(TTAGGG) repeat increased the Kd of complexes with uqTBP25 by 9-215-fold. Association with uqTBP25 protected d(TTAGGG)4 against nuclease digestion, suggesting a potential role for the protein in telomeric DNA transactions.
authors.affiliation: Unit of Biochemistry, The Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, P. O. Box 9649, Haifa 31096, Israel.
authors.forename: R
authors.initials: R
authors.lastname: Erlitzki
authors.forename: M
authors.initials: M
authors.lastname: Fry
mesh_terms: D000818:Animals; D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D054856:G-Quadruplexes; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D010449:Peptide Mapping; D051381:Rats; D012261:Ribonucleoproteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D016615:Telomere / Q000378:metabolism*
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D034441:Heterogeneous-Nuclear Ribonucleoproteins; C000619658:Hnrnpa1 protein, rat; D012261:Ribonucleoproteins; C439768:hnRNP A2; D004247:DNA