Previous Article | Next Article ![]()
Mol. Cell. Biol., Jan 1998, 240-249, Vol 18, No. 1
S Hayes, P Shiyanov, X Chen and P Raychaudhuri
The transcription factor E2F1 is believed to be involved in the regulated
expression of the DNA replication genes. To gain insights into the
transcriptional activation function of E2F1, we looked for proteins in HeLa
nuclear extracts that bind to the activation domain of E2F1. Here we show
that DDB, a putative DNA repair protein, associates with the activation
domain of E2F1. DDB was identified as a heterodimeric protein (48 and 127
kDa) that binds to UV-damaged DNA. We show that the UV-damaged-DNA binding
activity from HeLa nuclear extracts can associate with the activation
domain of E2F1. Moreover, the 48-kDa subunit of DDB, synthesized in vitro,
binds to a fusion protein of E2F1 depending on the C-terminal activation
domain. The interaction between DDB and E2F1 can also be detected by
coimmunoprecipitation experiments. Immunoprecipitation of an epitope-
tagged DDB from cell extracts resulted in the coprecipitation of E2F1. In a
reciprocal experiment, immunoprecipitates of E2F1 were found to contain
DDB. Fractionation of HeLa nuclear extracts also revealed a significant
overlap in the elution profiles of E2F1 and DDB. For instance, DDB, which
does not bind to the E2F sites, was enriched in the high-salt fractions
containing E2F1 during chromatography through an E2F-specific DNA affinity
column. We also observed evidence for a functional interaction between DDB
and E2F1 in living cells. For instance, expression of DDB specifically
stimulated E2F1-activated transcription. In addition, the transcriptional
activation function of a heterologous transcription factor containing the
activation domain of E2F1 was stimulated by coexpression of DDB. Moreover,
DDB expression could overcome the retinoblastoma protein (Rb)-mediated
inhibition of E2F1-activated transcription. The results suggest that this
damaged-DNA binding protein can function as a transcriptional partner of
E2F1. We speculate that the damaged-DNA binding function of DDB, besides
repair, might serve as a negative regulator of E2F1-activated
transcription, as damaged DNA will sequester DDB and make it unavailable
for E2F1. Furthermore, the binding of DDB to damaged DNA might be involved
in downregulating the replication genes during growth arrest induced by
damaged DNA.
Copyright © 1998, American Society for Microbiology
DDB, a putative DNA repair protein, can function as a transcriptional partner of E2F1
Department of Biochemistry and Molecular Biology, University of Illinois at Chicago, 60612, USA.
This article has been cited by other articles:
| J. Bacteriol. | J. Virol. | Eukaryot. Cell |
|---|
| Microbiol. Mol. Biol. Rev. | Clin. Vaccine Immunol. | All ASM Journals |
|---|