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Journal of Virology, March 2000, p. 2084-2093, Vol. 74, No. 5
Department of Molecular Genetics and
Microbiology, School of Medicine, State University of New York,
Stony Brook, New York 11794
Received 2 August 1999/Accepted 30 November 1999
The adenovirus type 5 (Ad5) E4-6/7 protein interacts directly with
different members of the E2F family and mediates the cooperative and
stable binding of E2F to a unique pair of binding sites in the Ad5 E2a
promoter region. This induction of E2F DNA binding activity strongly
correlates with increased E2a transcription when analyzed using virus
infection and transient expression assays. Here we show that while
different adenovirus isolates express an E4-6/7 protein that is capable
of induction of E2F dimerization and stable DNA binding to the Ad5 E2a
promoter region, not all of these viruses carry the inverted E2F
binding site targets in their E2a promoter regions. The Ad12 and Ad40
E2a promoter regions bind E2F via a single binding site. However, these
promoters bind adenovirus-induced (dimerized) E2F very weakly. The Ad3
E2a promoter region binds E2F very poorly, even via a single binding
site. A possible explanation of these results is that the Ad E4-6/7 protein evolved to induce cellular gene expression. Consistent with
this notion, we show that infection with different adenovirus isolates
induces the binding of E2F to an inverted configuration of binding
sites present in the cellular E2F-1 promoter. Transient expression of
the E4-6/7 protein alone in uninfected cells is sufficient to induce
transactivation of the E2F-1 promoter linked to chloramphenicol
acetyltransferase or green fluorescent protein reporter genes. Further,
expression of the E4-6/7 protein in the context of adenovirus infection
induces E2F-1 protein accumulation. Thus, the induction of E2F binding
to the E2F-1 promoter by the E4-6/7 protein observed in vitro
correlates with transactivation of E2F-1 promoter activity in vivo.
These results suggest that adenovirus has evolved two distinct
mechanisms to induce the expression of the E2F-1 gene. The E1A proteins
displace repressors of E2F activity (the Rb family members) and
thus relieve E2F-1 promoter repression; the E4-6/7 protein complements
this function by stably recruiting active E2F to the E2F-1 promoter to
transactivate expression.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Induction of the Cellular E2F-1 Promoter by the
Adenovirus E4-6/7 Protein

*
Corresponding author. Mailing address: Department of
Molecular Genetics and Microbiology, School of Medicine, State
University of New York, Stony Brook, NY 11794. Phone: (631) 632-8813. Fax: (631) 632-8891. E-mail: phearing{at}ms.cc.sunysb.edu.
Present address: Department of Anatomy, Howard Hughes Medical
Institute, University of California, San Francisco, CA 94143.
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