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J. Virol., 01 1998, 504-511, Vol 72, No. 1
Y Kang, WS Blair and BR Cullen
The transcription of genes carried by primate foamy viruses is dependent on
two distinct promoter elements. These are the long terminal repeat (LTR)
promoter, which regulates expression of the viral structural proteins, and
a second internal promoter, located towards the 3' end of the env gene,
that directs expression of the viral auxiliary proteins. One of these
auxiliary proteins is a potent transcriptional transactivator, termed Bel-1
in human foamy virus (HFV) and Tas or Taf in the related simian foamy
viruses, that is critical for foamy virus replication. Previously, it has
been demonstrated that the LTR promoter element of HFV contains a DNA
binding site for Bel-1 that is critical for transcriptional activation (F.
He, W. S. Blair, J. Fukushima, and B. R. Cullen, J. Virol. 70:3902-3908,
1996). Here, we extended this earlier work by using methylation
interference analysis to identify and characterize the Bel-1 DNA binding
sites located in the HFV LTR and internal promoter elements. Based on these
data, we propose a minimal, 25-bp DNA binding site for Bel-1, derived from
the HFV internal promoter element, and show that this short DNA sequence
mediates efficient Bel-1 binding both in vitro and in vivo. We further
demonstrate that, as determined by both in vitro and in vivo assays, the
Bel-1 target site located within the HFV internal promoter binds Bel-1 with
a significantly higher affinity than the cap-proximal Bel-1 target site
located in the LTR promoter. This result may provide a mechanistic
explanation for the observation that the internal promoter is activated
significantly earlier than the LTR promoter during the foamy virus life
cycle.
Copyright © 1998, American Society for Microbiology
Identification and functional characterization of a high-affinity Bel-1 DNA binding site located in the human foamy virus internal promoter
Department of Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA.
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