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J. Virol., 10 1995, 6038-6046, Vol 69, No. 10
ME Jackson and MS Campo
The bovine papillomavirus type 4 (BPV4) long control region (LCR) contains
three consensus binding sites, E2(1), E2(2), and E2(3) (ACCN6GGT), for the
viral E2 transcription factor and a fourth degenerate site, dE2 (ATCN6GGT),
which lies 3 bp upstream of E2(3). The E2(2) site was found to bind the
cellular transcription factor PEBP2, and mutations at this site reduced
basal promoter activity by as much as 60%, indicating an important role for
PEBP2 in LCR function. Mutation of the E2(3) or dE2 site slightly decreased
basal promoter activity, but the cellular proteins binding these sites have
not yet been characterized. E2 protein was found to have considerable
influence upon LCR promoter activity in primary bovine palate
keratinocytes. Thus, when high levels of BPV1 E2 were present, almost
complete repression of the BPV4 LCR was observed, whereas smaller amounts
of BPV1 or BPV4 E2 led to transactivation. Mutational analysis indicated
that E2(1) and dE2 mediated transactivation by E2, whereas E2(2) and E2(3)
were responsible for repression by E2. In vitro complexes of binding sites
E2(1) and E2(2) with E2 protein demonstrated much greater stability than
complexes formed by the E2(3) and dE2 sites. These data suggest that the
four E2 sites in the BPV4 LCR each perform different functions in the
control of transcription and that competition between cellular
transcription factors and viral E2 proteins is essential in regulating the
level of viral gene expression during papilloma development.
Copyright © 1995, American Society for Microbiology
Both viral E2 protein and the cellular factor PEBP2 regulate transcription via E2 consensus sites within the bovine papillomavirus type 4 long control region
Beatson Institute for Cancer Research, Beatson Laboratories, Bearsden, Glasgow, Scotland.
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