title: Site-specific DNA binding of the Schizosaccharomyces pombe origin recognition complex is determined by the Orc4 subunit.
abstract: The mechanism by which origin recognition complexes (ORCs) identify replication origins was investigated using purified Orc proteins from Schizosaccharomyces pombe. Orc4p alone bound tightly and specifically to several sites within S. pombe replication origins that are genetically required for origin activity. These sites consisted of clusters of A or T residues on one strand but were devoid of either alternating A and T residues or GC-rich sequences. Addition of a complex consisting of Orc1, -2, -3, -5, and -6 proteins (ORC-5) altered neither Orc4p binding to origin DNA nor Orc4p protection of specific sequences. ORC-5 alone bound weakly and nonspecifically to DNA; strong binding required the presence of Orc4p. Under these conditions, all six subunits remained bound to chromatin isolated from each phase of the cell division cycle. These results reveal that the S. pombe ORC binds to multiple, specific sites within replication origins and that site selection, at least in vitro, is determined solely by the Orc4p subunit.
authors.affiliation: National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-2753, USA.
authors.forename: D
authors.initials: D
authors.lastname: Kong
authors.forename: M L
authors.initials: ML
authors.lastname: DePamphilis
mesh_terms: D001483:Base Sequence / Q000502:physiology; D001665:Binding Sites / Q000502:physiology; D002453:Cell Cycle / Q000502:physiology; D002843:Chromatin / Q000378:metabolism; D004261:DNA Replication / Q000502:physiology; D004271:DNA, Fungal / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005656:Fungal Proteins / Q000378:metabolism; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D051738:Origin Recognition Complex; D011485:Protein Binding / Q000502:physiology; D021122:Protein Subunits; D012568:Schizosaccharomyces; D013379:Substrate Specificity
chemical_list: D002843:Chromatin; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D046911:Macromolecular Substances; D051738:Origin Recognition Complex; D021122:Protein Subunits