title: Dimeric structure of the Oxytricha nova telomere end-binding protein alpha-subunit bound to ssDNA.
abstract: Telomeres are the specialized protein--DNA complexes that cap and protect the ends of linear eukaryotic chromosomes. The extreme 3' end of the telomeric DNA in Oxytricha nova is bound by a two-subunit sequence-specific and 3' end-specific protein called the telomere end-binding protein (OnTEBP). Here we describe the crystal structure of the alpha-subunit of OnTEBP in complex with T4G4 single-stranded telomeric DNA. This structure shows an (alpha--ssDNA)2 homodimer with a large approximately 7,000 A2 protein--protein interface in which the domains of alpha are rearranged extensively from their positions in the structure of an alpha--beta--ssDNA ternary complex. The (alpha--ssDNA)2 complex can bind two telomeres on opposite sides of the dimer and, thus, acts as a protein mediator of telomere--telomere associations. The structures of the (alpha--ssDNA)2 dimer presented here and the previously described alpha--beta--ssDNA complex demonstrate that OnTEBP forms multiple telomeric complexes that potentially mediate the assembly and disassembly of higher order telomeric structures.
authors.affiliation: University of Colorado, Department of Chemistry and Biochemistry, Boulder, Colorado 80309-0215 USA. Olve.Peersen@ColoState.edu
authors.forename: Olve B
authors.initials: OB
authors.lastname: Peersen
authors.forename: James A
authors.initials: JA
authors.lastname: Ruggles
authors.forename: Steve C
authors.initials: SC
authors.lastname: Schultz
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004277:DNA, Single-Stranded / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D016813:Oxytricha / Q000737:chemistry / Q000235:genetics; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics; D016615:Telomere / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D021122:Protein Subunits; D015800:Protozoan Proteins