ICP4-binding sites in the promoter and coding regions of the herpes simplex virus gD gene contribute to activation of in vitro transcription by ICP4

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Abstract
The herpes simplex virus immediate-early gene product product ICP4 activates the transcriptions of viral early and late genes. We characterized the DNA sequence elements of the early glycoprotein D (gD) gene that play a role in the response to ICP4 in vitro. Using gel mobility shift assays and DNase I footprinting, we identified three ICP4-binding sites, two 5'' to the mRNA start site and a third within the coding region. Site II, which gave a footprint between nucleotides -75 and -111 relative to the RNA start site, was previously identified by Faber and Wilcox and contained the reported consensus ICP4-binding site. Site III, which was located between nucleotides +122 and +163, was very similar to the site II sequence, including a core consensus binding sequence, TCGTC. The site I sequence (nucleotides -308 to -282), however, did not share significant homology with either site II or site III. In vitro transcription experiments from mutant constructs of the gD promoter indicated that all thre ICP4-binding sites contribute to the stimulation of transcription by ICP4. DNase I footprinting of the gD promoter with uninfected nuclear extracts of HeLa cells showed protection of two very G-rich sequences between nucleotides -33 and -75. We propose that optimal transcription of the gD gene depends on the interaction of ICP4 with multiple binding sites across the gene and cellular factors that recognise specific sequence elements in the promoter.

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