title: Characterization of a novel origin recognition complex-like complex: implications for DNA recognition, cell cycle control, and locus-specific gene amplification.
abstract: The origin recognition complex (ORC) plays a central role in eukaryotic DNA replication. Here we describe a unique ORC-like complex in Tetrahymena thermophila, TIF4, which bound in an ATP-dependent manner to sequences required for cell cycle-controlled replication and gene amplification (ribosomal DNA [rDNA] type I elements). TIF4's mode of DNA recognition was distinct from that of other characterized ORCs, as it bound exclusively to single-stranded DNA. In contrast to yeast ORCs, TIF4 DNA binding activity was cell cycle regulated and peaked during S phase, coincident with the redistribution of the Orc2-related subunit, p69, from the cytoplasm to the macronucleus. Origin-binding activity and nuclear p69 immunoreactivity were further regulated during development, where they distinguished replicating from nonreplicating nuclei. Both activities were lost from germ line micronuclei following the programmed arrest of micronuclear replication. Replicating macronuclei stained with Orc2 antibodies throughout development in wild-type cells but failed to do so in the amplification-defective rmm11 mutant. Collectively, these findings indicate that the regulation of TIF4 is intimately tied to the cell cycle and developmentally programmed replication cycles. They further implicate TIF4 in rDNA gene amplification. As type I elements interact with other sequence-specific single-strand breaks (in vitro and in vivo), the dynamic interplay of Orc-like (TIF4) and non-ORC-like proteins with this replication determinant may provide a novel mechanism for regulation.
authors.affiliation: Department of Medical Biochemistry and Genetics, Texas A&M Health Science Center, College Station, Texas 77843-1114, USA.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Mohammad
authors.forename: Randall D
authors.initials: RD
authors.lastname: York
authors.forename: Jonathan
authors.initials: J
authors.lastname: Hommel
authors.forename: Geoffrey M
authors.initials: GM
authors.lastname: Kapler
mesh_terms: D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle / Q000235:genetics*; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D005784:Gene Amplification; D018507:Gene Expression Regulation, Developmental; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009154:Mutation; D051738:Origin Recognition Complex; D021122:Protein Subunits; D015800:Protozoan Proteins; D016808:Tetrahymena thermophila / Q000166:cytology / Q000235:genetics; D014981:Xenopus
chemical_list: D002843:Chromatin; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D051738:Origin Recognition Complex; D021122:Protein Subunits; D015800:Protozoan Proteins; C443134:TIF1 protein, Tetrahymena thermophila; D004247:DNA