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The stage of herpes simplex virus (HSV) replication responsible for the transcriptional activation of Alu repeats by RNA polymerase Ⅲ was investigated. The induction of Alu repeats started at a quite early stage of infection and, like a viral early gene, required viral protein synthesis but not viral DNA replication. The effect was still observed in infections with various HSV-1 mutants such as dl1403, tsK, R325, and N38-carrying mutations in the immediate early genes encoding ICP0, ICP4, ICP22, and ICP47, respectively. It was abolished in infection with the HSV-1 mutant 17 × 2D, which carries a mutation in the gene encoding ICP27. This indicates that ICP27 is responsible for the induction of Alu transcription. This induction does not require the full lytic cycle, as the ICP27 protein expressed from the transiently transfected gene was sufficient to induce this effect. The possible mechanism of this effect and its significance during HSV-1 infection are proposed.
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