Identification and functional characterization of a new member of the human Mcm protein family: hMcm8
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Devrim Gozuacik1, Mounia Chami, David Lagorce
1INSERM Unit 370/Pasteur Institute, Faculté de Médecine Necker-Enfants Malades, 156 rue de Vaugirard, 75730, Paris, France.
Abstract:
The six minichromosome maintenance proteins (Mcm2-7) are required for both the initiation and elongation of chromosomal DNA, ensuring that DNA replication takes place once, and only once, during the S phase. Here we report on the cloning of a new human Mcm gene (hMcm8) and on characterisation of its protein product. The hMcm8 gene contains the central Mcm domain conserved in the Mcm2-7 gene family, and is expressed in a range of cell lines and human tissues. hMcm8 mRNA accumulates during G(1)/S phase, while hMcm8 protein is detectable throughout the cell cycle. Immunoprecipitation-based studies did not reveal any participation of hMcm8 in the Mcm3/5 and Mcm2/4/6/7 subcomplexes. hMcm8 localises to the nucleus, although it is devoid of a nuclear localisation signal, suggesting that it binds to a nuclear protein. In the nucleus, the hMcm8 structure-bound fraction is detectable in S, but not in G(2)/M, phase, as for hMcm3. However, unlike hMcm3, the hMcm8 structure-bound fraction is not detectable in G(1) phase. Overall, our data identify a new Mcm protein, which does not form part of the Mcm2-7 complex and which is only structure-bound during S phase, thus suggesting its specific role in DNA replication.
Insights
Researchers identified a new human protein, hMcm8, crucial for DNA replication. This protein, distinct from the Mcm2-7 complex, specifically binds during S phase, suggesting a unique role in cell division.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- The minichromosome maintenance (Mcm2-7) proteins are essential for accurate DNA replication during the S phase.
- Ensuring DNA replication occurs only once per cell cycle is critical for genomic stability.
Purpose of the Study:
- To clone and characterize a novel human Mcm protein, designated hMcm8.
- To investigate the cellular localization, expression patterns, and potential function of hMcm8 in DNA replication.
Main Methods:
- Gene cloning and protein characterization of hMcm8.
- Analysis of hMcm8 mRNA and protein expression across cell lines and tissues.
- Immunoprecipitation assays to determine hMcm8 complex formation.
- Cell cycle analysis of hMcm8 localization and structure-bound fraction.
Main Results:
- hMcm8 possesses a conserved Mcm domain and is expressed in various human cells and tissues.
- hMcm8 mRNA levels peak during G1/S phase, while the protein is present throughout the cell cycle.
- hMcm8 does not associate with the known Mcm2-7 subcomplexes (Mcm3/5 and Mcm2/4/6/7).
- hMcm8 localizes to the nucleus and its structure-bound fraction is detectable only during S phase, unlike hMcm3.
Conclusions:
- hMcm8 represents a novel Mcm protein that functions independently of the core Mcm2-7 replication complex.
- The cell cycle-specific binding of hMcm8 during S phase suggests a specialized role in DNA replication initiation or elongation.
- Further research into hMcm8 could uncover new mechanisms regulating DNA replication fidelity.
