J. Virol., 09 1995, 5209-5216, Vol 69, No. 9
V Misra, S Walker, S Hayes and P O'Hare
In herpes simplex virus (HSV)-infected cells, viral gene expression is
initiated when the immediate-early, or alpha, genes are transactivated by
the alpha gene trans-inducing factor (alpha TIF), a component of the
infecting virion. The protein binds to one or more recognition elements
(TAATGARAT) in the promoters of alpha genes via interaction with the
cellular proteins Oct-1 and CFF. The alpha TIF of HSV (HSV-alpha TIF) is
believed to subsequently accelerate the assembly of the transcription
complex by direct contact between its carboxyl-terminal acidic activation
domain and at least two components of the transcription apparatus, TAFII40
and TFIIB. Like its HSV counterpart, the alpha TIF of bovine herpesvirus
(BHV) (designated BHV-alpha TIF) also transactivates alpha gene promoters
and for full activity exhibits a requirement for its extended
carboxyl-terminal region. Despite this requirement, there is a notable lack
of homology to the carboxyl- terminal acidic activation domain of HSV-alpha
TIF. We swapped the amino- and carboxyl-terminal domains of HSV-alpha TIF
and BHV-alpha TIF to make chimeric proteins. Using these chimeras, we show
that the carboxyl terminus of BHV-alpha TIF is insufficient for
transactivation, which requires cooperative determinants in both the
amino-terminal and carboxyl-terminal regions of the protein. We have
previously shown that the amino-terminal determinant in BHV-alpha TIF
displays reduced but significant independent transactivation potential.
Interestingly, this amino-terminal determinant appears not to reside in the
HSV-alpha TIF, which displays no independent amino-terminal activity.
Furthermore, we show that the amino-terminal activation domain of BHV-alpha
TIF may be able to act synergistically with the carboxyl-terminal
activation domain of HSV-alpha TIF, since a chimeric protein containing
both domains appeared to be more efficient at activating transcription than
either alpha TIF. In addition, the amino terminus of HSV-alpha TIF could
not restore activity when linked to the carboxyl terminus of BHV- alpha
TIF, while the amino terminus of BHV-alpha TIF reconstituted an intact
protein with potent activation potential. We also show that in fusions with
the DNA binding domain of GAL4, full activity requires the entire BHV-alpha
TIF, although both amino and carboxyl termini display some activity on
their own. In contrast, for HSV-alpha TIF, the carboxyl terminus is
sufficient and possibly even more potent than the entire protein, while the
amino-terminus is devoid of activity.(ABSTRACT TRUNCATED AT 400 WORDS)
Copyright © 1995, American Society for Microbiology
The bovine herpesvirus alpha gene trans-inducing factor activates transcription by mechanisms different from those of its herpes simplex virus type 1 counterpart VP16
Department of Veterinary Microbiology, W.C.V.M. University of Saskatchewan, Saskatoon, Canada.
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