High impact information on CDC46

• A family of related yeast replication proteins, MCM2, 3 and 5 (also called, after cell-division cycle, CDC46), resemble licensing factor, entering the nucleus only during mitosis [1].
• Here, we show that the other genes, like CDC46, are all involved in an early step of DNA replication, possibly initiation of DNA synthesis [2].
• The DNA sequence of the CDC46 gene indicates that the protein is a member of a new family of genes apparently required for DNA initiation, with family members now identified in Saccharomyces cerevisiae, Schizosaccharomyces pombe, and mouse cells [2].
• Subcellular localization of yeast CDC46 varies with the cell cycle [3].
• We propose that the CDC46 protein, which is required for DNA replication, becomes mobilized quickly from the cytoplasm into the nucleus as mitosis is completed and persists there until the next round of division is initiated [3].

Biological context of CDC46

• CDC45 genetically interacts with at least two members of the MCM (minichromosome maintenance) family of replication genes, CDC46 and CDC47, which are proposed to perform a role in restricting initiation of DNA replication to once per cell cycle [4].
• CDC54 is a gene essential for initiation of DNA replication in Saccharomyces cerevisiae, and which is known to genetically interact with other regulators of the S-phase, including CDC46 [5].
• Mcm3-1 contains a G246E mutation that diminishes the efficiency of replication initiation (Yan, H., Merchant, A. M., and Tye, B. K. (1993) Genes Dev. 7, 2149-2160) but not its interaction with Mcm5 or recruitment of the MCM2-7 complex to replication origin [6].
• Molecular experiments revealed that the mcm5-bob1 mutation allows for constitutive loading of Cdc45p at early origins in arrested G1 phase cells when both kinases are inactive [7].
• A model is proposed in which the Mcm5-bob1 protein assumes a unique molecular conformation without prior action by either kinase [7].

Associations of CDC46 with chemical compounds

• When MCM5 cDNA was reintroduced into fresh TR9-7ER cells, numerous colonies that grow in the absence of tetracycline were formed [8].

Physical interactions of CDC46

• Cdc45p assembles into a complex with Cdc46p/Mcm5p, is required for minichromosome maintenance, and is essential for chromosomal DNA replication [4].
• The assembly of Cdc47p into complexes with Cdc46p does not appear to be cell cycle regulated, making it unlikely that these interactions per se are a rate-limiting step in the control of S phase [9].

Regulatory relationships of CDC46

• Genetic experiments revealed that loss of either Clb5p or Clb2p cyclins suppresses the mcm5-bob1 mutation and prevents bypass [7].

Other interactions of CDC46

• We characterize two mutations in CDC47 and CDC46 which arrest cells with unduplicated DNA as a result of single base substitutions [9].
• Mcm3-10 contains a P118L substitution that compromises its interaction with Mcm5 and the recruitment of Mcm3 and Mcm7 to a replication origin [6].
• These include the Saccharomyces cerevisiae MCM2 and MCM3 proteins, which are needed for the efficient function of certain replication origins, and S.cerevisiae CDC46, which is required for the initiation of chromosome replication [10].
• Finally, activation of the DNA damage checkpoint and the resulting cell cycle delay is intact in cdc7Delta mcm5-bob1 cells, suggesting a direct role for CDC7 in DNA repair/damage tolerance [11].
• Rereplication from origins requires both Cdc6p and Cdc46/Mcm5p, initiation proteins that had been thought to be inactivated by the Cdc28p kinase [12].

Analytical, diagnostic and therapeutic context of CDC46

• The cDNA was used as a probe for chromosomal fluorescence in situ hybridization (FISH), which localized the human Cdc46 gene (CDC46) to chromosome region 22q13.1-->q13 [13].
• The Csm1p-Mcm3, Mcm5 and Mcm7p interactions were confirmed by co-immunoprecipitation [14].
• Immunoblotting results demonstrate that mouse homologues of Mcm2, Mcm5, and Cdc6 are displaced from chromatin in quiescent cells [15].
• Using a chromatin immunoprecipitation assay (CHIP), we found that cdc6-1 fails to load Mcm5 onto the replication origins [16].
• Northern and Western blot analyses revealed that the expression of MCM5 and its transcriptional regulator, E2F1, is negatively regulated by p53 [8].

References