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The Rix1 (Ipi1p-2p-3p) complex is a critical determinant of DNA replication licensing independent of their roles in ribosome biogenesis.

Several replication-initiation proteins are assembled stepwise onto replicators to form pre-replicative complexes (pre-RCs) to license eukaryotic DNA replication. We performed a yeast functional proteomic screen and identified the Rix1 complex members (Ipi1p-Ipi2p/Rix1-Ipi3p) as pre-RC components and critical determinants of replication licensing and replication-initiation frequency. Ipi3p interacts with pre-RC proteins, binds chromatin predominantly at ARS sequences in a cell cycle-regulated and ORC- and Noc3p-dependent manner and is required for loading Cdc6p, Cdt1p and MCM onto chromatin to form pre-RC during the M-to-G₁ transition and for pre-RC maintenance in G₁ phase-independent of its role in ribosome biogenesis. Moreover, Ipi1p and Ipi2p, but not other ribosome biogenesis proteins Rea1p and Utp1p, are also required for pre-RC formation and maintenance, and Ipi1p, -2p and -3p are interdependent for their chromatin association and function in pre-RC formation. These results establish a new framework for the hierarchy of pre-RC proteins, where the Ipi1p-2p-3p complex provides a critical link between ORC-Noc3p and Cdc6p-Cdt1p-MCM in replication licensing.

Pubmed ID: 22421151


  • Huo L
  • Wu R
  • Yu Z
  • Zhai Y
  • Yang X
  • Chan TC
  • Yeung JT
  • Kan J
  • Liang C


Cell cycle (Georgetown, Tex.)

Publication Data

April 1, 2012

Associated Grants


Mesh Terms

  • Cell Cycle
  • Cell Cycle Proteins
  • Chromatin
  • DNA Helicases
  • DNA Replication
  • DNA-Binding Proteins
  • G1 Phase
  • Minichromosome Maintenance 1 Protein
  • Nuclear Proteins
  • Nucleocytoplasmic Transport Proteins
  • Origin Recognition Complex
  • Proteome
  • Replication Origin
  • Ribosomes
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Trans-Activators