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J. Virol., 05 1995, 3042-3048, Vol 69, No. 5
R Leopardi, N Michael and B Roizman
Infected cell protein no. 4 (ICP4), the major regulatory protein encoded by
the alpha 4 gene of herpes simplex virus 1, binds to a site (alpha 4-2) at
the transcription initiation site of the alpha 4 gene. An earlier report
described the construction of recombinant viruses that contained chimeric
genes (alpha 4-tk) that consisted of the 5' untranscribed and transcribed
noncoding domains of the alpha 4 gene fused to the coding sequences of the
thymidine kinase gene and showed that disruption of the alpha 4-2 binding
site by mutagenesis derepressed transcription of this gene (N. Michael and
B. Roizman, Proc. Natl. Acad. Sci. USA 90:2286-2290, 1993). This
experimental design was used to determine the effect of displacement of the
alpha 4- 2 binding site on the repression of alpha 4 gene transcription by
ICP4. We report the following findings. (i) In the absence of the alpha 4-2
binding site, at 4 h after infection, alpha 4-tk RNA levels increased
10-fold relative to the corresponding RNA levels of a gene that contained
the alpha 4-2 site at its natural location. Displacement of the alpha 4-2
binding site by approximately one, two, and three turns of the DNA helix,
i.e., by 10, 21, and 30 nucleotides downstream of the original site,
increased the concentration of alpha 4-tk RNA 2.4-, 3.5- , and 5.8-fold,
respectively. (ii) Displacement of 16 nucleotides, i.e., approximately 1.5
helical turns, increased the accumulation of alpha 4-tk by 5.3-fold, i.e.,
more than predicted by displacement alone. (iii) At 8 h after infection in
the absence of the binding site, the accumulation of alpha 4-tk RNA
increased 13.6-fold. However, in cells infected with recombinants that
carried displaced alpha 4-2 binding sites, RNA accumulation decreased
relative to the levels seen at 4 h after infection. The insertion of DNA
sequences in order to displace the alpha 4-2 binding site had no effect on
accumulation of RNA in the presence of cycloheximide, i.e., in the absence
of ICP4, or on maximum accumulation of alpha 4-tk RNA in the absence of the
alpha 4- 2 binding site.(ABSTRACT TRUNCATED AT 400 WORDS)
Copyright © 1995, American Society for Microbiology
Repression of the herpes simplex virus 1 alpha 4 gene by its gene product (ICP4) within the context of the viral genome is conditioned by the distance and stereoaxial alignment of the ICP4 DNA binding site relative to the TATA box
Marjorie B. Kovler Viral Oncology Laboratories, University of Chicago, Illinois 60637, USA.
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