Nuclear organization of DNA replication initiation proteins in mammalian cells

Masatoshi Fujita, Yukio Ishimi, Hiromu Nakamura, Tohru Kiyono, Tatsuya Tsurumi

Research output: Contribution to journalArticle

65 Citations (Scopus)

Abstract

Origin recognition complex (ORC), CDC6, and MCM proteins assemble sequentially to form prereplication chromatin. However, their organization remains largely unclear in mammalian cells. Here we show that ORC1 proteins are associated with non-chromatin nuclear structures and assemble in nuclear foci in mammalian cells using an in vivo chemical cross-linking method. CDC6 proteins were also found to assemble in nuclear foci on non-chromatin nuclear structures, although their physical association with ORC1 has been undetectable. In contrast to the situation in yeast cells, CDC6 was found to remain associated with non-chromatin nuclear structures even after cells entered into S phase. Instead, ORC1 proteins were found to be degraded by a proteasome-dependent pathway during S phase. We also found that some ORC2 proteins are associated with non-chromatin nuclear structures like ORC1, although the remainder binds to nuclease-sensitive chromatin. Further analyses indicate that ORC2 physically interacts with ORC1 on non-chromatin nuclear structures. On the other hand, our results suggest that although a small proportion of MCM complexes are loaded onto chromatin regions near ORC foci, most of them are more widely distributed. Possible relations between such organization of prereplication chromatin and complicated origin specification in higher eukaryotic cells are discussed.

Original languageEnglish
Pages (from-to)10354-10361
Number of pages8
JournalJournal of Biological Chemistry
Volume277
Issue number12
DOIs
Publication statusPublished - Mar 22 2002
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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