title: Xenopus origin recognition complex (ORC) initiates DNA replication preferentially at sequences targeted by Schizosaccharomyces pombe ORC.
abstract: Budding yeast (Saccharomyces cerevisiae) origin recognition complex (ORC) requires ATP to bind specific DNA sequences, whereas fission yeast (Schizosaccharomyces pombe) ORC binds to specific, asymmetric A:T-rich sites within replication origins, independently of ATP, and frog (Xenopus laevis) ORC seems to bind DNA non-specifically. Here we show that despite these differences, ORCs are functionally conserved. Firstly, SpOrc1, SpOrc4 and SpOrc5, like those from other eukaryotes, bound ATP and exhibited ATPase activity, suggesting that ATP is required for pre-replication complex (pre-RC) assembly rather than origin specificity. Secondly, SpOrc4, which is solely responsible for binding SpORC to DNA, inhibited up to 70% of XlORC-dependent DNA replication in Xenopus egg extract by preventing XlORC from binding to chromatin and assembling pre-RCs. Chromatin-bound SpOrc4 was located at AT-rich sequences. XlORC in egg extract bound preferentially to asymmetric A:T-sequences in either bare DNA or in sperm chromatin, and it recruited XlCdc6 and XlMcm proteins to these sequences. These results reveal that XlORC initiates DNA replication preferentially at the same or similar sites to those targeted in S.pombe.
authors.affiliation: National Institute of Child Health and Human Development, Building 6/416, 9000 Rockville Pike, National Institutes of Health, Bethesda, MD 20892-2753, USA.
authors.forename: Daochun
authors.initials: D
authors.lastname: Kong
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Coleman
authors.forename: Melvin L
authors.initials: ML
authors.lastname: DePamphilis
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D004261:DNA Replication / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology*; D006868:Hydrolysis; D051738:Origin Recognition Complex; D011485:Protein Binding; D012568:Schizosaccharomyces / Q000235:genetics*; D014982:Xenopus laevis
chemical_list: D004268:DNA-Binding Proteins; D051738:Origin Recognition Complex; D000255:Adenosine Triphosphate