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Mol. Cell. Biol., Apr 1997, 1890-1903, Vol 17, No. 4
ER Fernandes and RJ Rooney
A 50-kDa cellular factor, E4F, has been implicated in mediating trans
activation of the adenovirus E4 gene by the 289R E1A(13S) protein. Previous
experiments demonstrated an E1A-dependent increase in E4F DNA binding
activity, dependent on phosphorylation, that correlated with the activation
of E4 transcription. Using expression screening, we isolated a cDNA clone
encoding the E4F protein, as judged by DNA binding characteristics,
transcriptional activation, and immunological criteria. The E4F-1 cDNA
encodes a 783-amino-acid polypeptide that has 86% sequence identity with
the murine nuclear factor phiAP3, a GLI- kruppel-related protein. E4F DNA
binding activity is encoded within an amino-terminal region of E4F-1 that
contains a zinc finger domain and, as with endogenous E4F, is phosphatase
sensitive. We found that E4F was generated from the full-length
E4F-1-encoded protein as a 50-kDa amino- terminal fragment. Moreover,
E1A(13S) expression induced the phosphorylation of both forms of E4F-1 but
differentially regulated their DNA binding activities, stimulating the
50-kDa fragment while reducing the activity of the full-length protein. In
transient- transfection assays, the E4F-1 amino-terminal fragment
stimulated the adenovirus E4 promoter in the presence of E1A(13S), whereas
the full- length protein repressed the promoter in the absence, but not the
presence, of E1A. The results indicate that the 50-kDa polypeptide
responsible for E4F DNA binding activity is a fragment generated from the
human homolog of phiAP3 and that the two forms of the E4F-1 protein are
differentially regulated by E1A through phosphorylation.
Copyright © 1997, American Society for Microbiology
The adenovirus E1A-regulated transcription factor E4F is generated from the human homolog of nuclear factor phiAP3
Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
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