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CDF-1, a novel E2F-unrelated factor, interacts with cell cycle-regulated repressor elements in multiple promoters
N Liu1, F C Lucibello, K Körner
1Institut für Molekularbiologie und Tumorforschung (IMT), Philipps-Universität Marburg Emil-Mannkopff-Strasse 2, D-35033 Marburg, Germany.
Abstract:
The cdc25C , cdc2 and cyclin A promoters are controlled by transcriptional repression through two contiguous protein binding sites, termed the CDE and CHR. In the present study we have identified a factor, CDF-1, which interacts with the cdc25C CDE-CHR module. CDF-1 binds to the CDE in the major groove and to the CHR in the minor grove in a cooperative fashion in vitro , in a manner similar to that seen by genomic footprinting. In agreement with in vivo binding data and its putative function as a periodic repressor, DNA binding by CDF-1 in nuclear extracts is down-regulated during cell cycle progression. CDF-1 also binds avidly to the CDE-CHR modules of the cdc2 and cyclin A promoters, but not to the E2F site in the B- myb promoter. Conversely, E2F complexes do not recognize the cdc25C CDE-CHR and CDF-1 is immunologically unrelated to all known E2F and DP family members. This indicates that E2F- and CDF-mediated repression is controlled by different factors acting at different stages during the cell cycle. While E2F-mediated repression seems to be associated with genes that are up-regulated early (around mid G1), such as B- myb , CDE-CHR-controlled genes, such as cdc25C , cdc2 and cyclin A , become derepressed later. Finally, the fractionation of native nuclear extracts on glycerol gradients leads to separation of CDF-1 from both E2F complexes and pocket proteins of the pRb family. This emphasizes the conclusion that CDF-1 is not an E2F family member and points to profound differences in the cell cycle regulation of CDF-1 and E2F.
Insights
A novel protein, CDF-1, represses cell cycle genes like cdc25C by binding to CDE-CHR sites. Its activity decreases during the cell cycle, distinct from E2F regulation.
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- Transcriptional Regulation
Background:
- The promoters of cdc25C, cdc2, and cyclin A are transcriptionally repressed.
- This repression is mediated by two adjacent protein-binding sites: CDE and CHR.
Purpose of the Study:
- To identify and characterize the factor that interacts with the cdc25C CDE-CHR module.
- To elucidate the role of this factor in cell cycle-regulated gene expression.
Main Methods:
- In vitro DNA binding assays to study CDF-1 interaction with CDE-CHR.
- Genomic footprinting to confirm binding patterns.
- Analysis of CDF-1 binding in nuclear extracts during cell cycle progression.
- Glycerol gradient fractionation to separate CDF-1 from other factors.
Main Results:
- A novel factor, CDF-1, was identified, binding cooperatively to the CDE and CHR sites.
- CDF-1 binding is down-regulated during cell cycle progression, consistent with a periodic repressor role.
- CDF-1 binds to cdc25C, cdc2, and cyclin A promoters but not the B-myb promoter's E2F site.
- CDF-1 is immunologically distinct from E2F and DP proteins and separates from E2F/pRb complexes.
Conclusions:
- CDF-1 is a novel repressor of cell cycle genes, distinct from the E2F family.
- CDF-1 and E2F regulate different sets of genes at different cell cycle stages.
- This discovery reveals distinct mechanisms for cell cycle control of gene transcription.