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Molecular and Cellular Biology, November 1998, p. 6679-6697, Vol. 18, No. 11
Department of Experimental Oncology, European
Institute of Oncology, 20141 Milan, Italy,1
and
Institut de Génétique Moléculaire,
CNRM, UMR 5535, 34033 Montpellier Cedex 1, France2
Received 20 February 1998/Returned for modification 13 April
1998/Accepted 18 August 1998
The E2F transcription factors are essential regulators of cell
growth in multicellular organisms, controlling the expression of a
number of genes whose products are involved in DNA replication and cell
proliferation. In Saccharomyces cerevisiae, the MBF and SBF
transcription complexes have functions similar to those of E2F proteins
in higher eukaryotes, by regulating the timed expression of genes
implicated in cell cycle progression and DNA synthesis. The
CDC6 gene is a target for MBF and SBF-regulated
transcription. S. cerevisiae Cdc6p induces the formation of
the prereplication complex and is essential for initiation of DNA
replication. Interestingly, the Cdc6p homolog in
Schizosaccharomyces pombe, Cdc18p, is regulated by DSC1,
the S. pombe homolog of MBF. By cloning the promoter for
the human homolog of Cdc6p and Cdc18p, we demonstrate here that the
cell cycle-regulated transcription of this gene is dependent on E2F. In
vivo footprinting data demonstrate that the identified E2F sites are
occupied in resting cells and in exponentially growing cells,
suggesting that E2F is responsible for downregulating the promoter in
early phases of the cell cycle and the subsequent upregulation when
cells enter S phase. Our data also demonstrate that the human CDC6
protein (hCDC6) is essential and limiting for DNA synthesis, since
microinjection of an anti-CDC6 rabbit antiserum blocks DNA synthesis
and CDC6 cooperates with cyclin E to induce entry into S phase in
cotransfection experiments. Furthermore, E2F is sufficient to induce
expression of the endogenous CDC6 gene even in the absence
of de novo protein synthesis. In conclusion, our results provide a
direct link between regulated progression through G1
controlled by the pRB pathway and the expression of proteins essential
for the initiation of DNA replication.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Cell Cycle-Regulated Expression of Mammalian
CDC6 Is Dependent on E2F

*
Corresponding author. Mailing address: Department of
Experimental Oncology, European Institute of Oncology, Via Ripamonti 435, 20141 Milan, Italy. Phone: 39 02 5748 9860. Fax: 39 02 5748 9851. E-mail: khelin{at}ieo.cilea.it.
Present address: IntroGene, 2333 AL Leiden, The Netherlands.
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