title: Orc1 Binding to Mitotic Chromosomes Precedes Spatial Patterning during G1 Phase and Assembly of the Origin Recognition Complex in Human Cells.
abstract: Replication of eukaryotic chromosomes occurs once every cell division cycle in normal cells and is a tightly controlled process that ensures complete genome duplication. The origin recognition complex (ORC) plays a key role during the initiation of DNA replication. In human cells, the level of Orc1, the largest subunit of ORC, is regulated during the cell division cycle, and thus ORC is a dynamic complex. Upon S phase entry, Orc1 is ubiquitinated and targeted for destruction, with subsequent dissociation of ORC from chromosomes. Time lapse and live cell images of human cells expressing fluorescently tagged Orc1 show that Orc1 re-localizes to condensing chromatin during early mitosis and then displays different nuclear localization patterns at different times during G1 phase, remaining associated with late replicating regions of the genome in late G1 phase. The initial binding of Orc1 to mitotic chromosomes requires C-terminal amino acid sequences that are similar to mitotic chromosome-binding sequences in the transcriptional pioneer protein FOXA1. Depletion of Orc1 causes concomitant loss of the mini-chromosome maintenance (Mcm2-7) helicase proteins on chromatin. The data suggest that Orc1 acts as a nucleating center for ORC assembly and then pre-replication complex assembly by binding to mitotic chromosomes, followed by gradual removal from chromatin during the G1 phase.
authors.affiliation: From the Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, the Graduate Program in Molecular and Cellular Biology, Stony Brook University, Stony Brook, New York 11779, and.
authors.forename: Nihan
authors.initials: N
authors.lastname: Kara
authors.affiliation: From the Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724.
authors.forename: Manzar
authors.initials: M
authors.lastname: Hossain
authors.affiliation: From the Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, the Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana-Champaign, Illinois 61801.
authors.forename: Supriya G
authors.initials: SG
authors.lastname: Prasanth
authors.affiliation: From the Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, stillman@cshl.edu.
authors.forename: Bruce
authors.initials: B
authors.lastname: Stillman
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000737:chemistry; D002455:Cell Division; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002875:Chromosomes / Q000648:ultrastructure; D004261:DNA Replication; D000939:Epitopes / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry; D016193:G1 Phase / Q000235:genetics; D015894:Genome, Human; D006367:HeLa Cells; D051541:Hepatocyte Nuclear Factor 3-alpha / Q000378:metabolism; D006801:Humans; D008938:Mitosis; D008969:Molecular Sequence Data; D051738:Origin Recognition Complex / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D017386:Sequence Homology, Amino Acid
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; C496499:FOXA1 protein, human; D005456:Fluorescent Dyes; D051541:Hepatocyte Nuclear Factor 3-alpha; C497223:ORC1 protein, human; D051738:Origin Recognition Complex
keywords: Cell Cycle; DNA Replication; DNA-binding Protein; FOXA1; Mitosis; Origin Recognition Complex; Protein-DNA Interaction