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Molecular and Cellular Biology, May 2000, p. 3626-3632, Vol. 20, No. 10
Department of Genetics, Howard Hughes Medical
Institute, Duke University Medical Center, Durham, North Carolina
27710
Received 29 October 1999/Returned for modification 23 November
1999/Accepted 22 February 2000
The tumor suppressor function of Rb is intimately related to its
ability to interact with E2F and repress the transcription of E2F
target genes. Here we describe a novel E2F product that specifically
interacts with Rb in quiescent cells. This novel E2F, which we term
E2F3b, is encoded by a unique mRNA transcribed from an intronic
promoter within the E2F3 locus. The E2F3b RNA differs from the
previously characterized E2F3 RNA, which we now term E2F3a, by the
utilization of a unique coding exon. In contrast to the E2F3a product
that is tightly regulated by cell growth, the E2F3b product is
expressed equivalently in quiescent and proliferating cells. But,
unlike the E2F4 and E2F5 proteins, which are also expressed in
quiescent cells and form complexes with the p130 protein, the E2F3b
protein associates with Rb and represents the predominant E2F-Rb
complex in quiescent cells. Thus, the previously described specificity
of Rb function as a transcriptional repressor in quiescent cells
coincides with the association of Rb with this novel E2F product.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Identification of a Novel E2F3 Product Suggests a Mechanism for
Determining Specificity of Repression by Rb Proteins


*
Corresponding author. Mailing address: Department of
Genetics, Howard Hughes Medical Institute, Duke University Medical
Center, Durham, NC 27710. Phone: (919) 684-2746. Fax: (919) 681-8973. E-mail: J.Nevins{at}duke.edu.
Present address: Division of Human Cancer Genetics, Ohio State
University, Columbus, OH 43210.
Present address: Abbott Laboratories, Abbott Park, IL 60064.
§
Present address: Department of Cancer Biology, Dana Farber Cancer
Institute, Boston, MA 02115.
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