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Drosophila MCM protein complexes
T T Su1, G Feger, P H O'Farrell
1Department of Biochemistry and Biophysics, University of California San Francisco 94143-0448, USA.
Abstract:
MCM genes encode a family of evolutionarily conserved proteins required for DNA replication. In Saccharomyces cerevisiae, where they were first identified, MCM genes interact genetically with each other. Allele specificity in these interactions suggests that MCM proteins physically associate with one another and that this association is essential for function. We describe here an analysis of physical interactions among three Drosophila MCM proteins. Using specific antibodies we detect Drosophila MCMs almost exclusively in 600-kDa protein complexes. Co-immunoprecipitation data demonstrate the existence of at least two distinct types of 600-kDa complexes, one that contains DmCDC46 and one that appears to contain both DmMCM2 and Dpa (a CDC54 homologue). These complexes are stable throughout embryonic division cycles, are resistant to treatments with salt and detergent, and are present during development in tissues undergoing mitotic DNA replication as well as endoreplication. When extracts are prepared under low salt conditions all three MCM proteins co-immunoprecipitate. Consequently, we suggest that the 600-kDa complexes interact in a higher order complex.
Insights
Drosophila MCM proteins form stable 600-kDa complexes essential for DNA replication. These complexes, containing DmCDC46 or DmMCM2/Dpa, suggest a higher-order assembly for replication function.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- MCM genes encode conserved proteins crucial for DNA replication.
- Genetic interactions in yeast suggest MCM proteins physically associate.
- This physical association is vital for MCM protein function.
Purpose of the Study:
- To analyze physical interactions among three Drosophila MCM proteins.
- To investigate the composition and stability of MCM protein complexes.
- To understand the role of MCM complexes in DNA replication.
Main Methods:
- Antibody-based detection of Drosophila MCM proteins.
- Co-immunoprecipitation assays to identify protein interactions.
- Analysis of protein complexes under various conditions (salt, detergent).
Main Results:
- Drosophila MCM proteins are found in stable 600-kDa complexes.
- Two distinct 600-kDa complexes identified: one with DmCDC46, another with DmMCM2 and Dpa.
- These complexes are stable during embryonic divisions and resistant to salt/detergent.
- All three MCM proteins co-immunoprecipitate under low salt conditions, indicating higher-order interactions.
Conclusions:
- Drosophila MCM proteins exist in distinct, stable protein complexes.
- These complexes likely assemble into a higher-order structure for DNA replication.
- The findings provide insights into the molecular mechanisms of DNA replication in Drosophila.