The adenovirus E1A-regulated transcription factor E4F is generated from the human homolog of nuclear factor phiAP3.
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-krüppel-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.
Fernandes
E R
ER
Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Rooney
R J
RJ
D017500:Adenovirus E1A Proteins / Q000235:genetics* / Q000378:metabolism*; D017504:Adenovirus E4 Proteins / Q000235:genetics / Q000378:metabolism; D000260:Adenoviruses, Human / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D051268:GA-Binding Protein Transcription Factor; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation; D044767:Ubiquitin-Protein Ligases
D017500:Adenovirus E1A Proteins; D017504:Adenovirus E4 Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C079860:E4TF1 transcription factor; D051268:GA-Binding Protein Transcription Factor; D012097:Repressor Proteins; D014157:Transcription Factors; C411663:transcription factor p120(E4F); D004247:DNA; C084953:E4f1 protein, mouse; D044767:Ubiquitin-Protein Ligases