Regulation of herpes simplex virus 1 genes: α gene sequence requirements for transient induction of indicator genes regulated by β or late ( γ2) promoters

Abstract

This laboratory reported earlier that chimeric genes consisting of the structural sequences of the thymidine kinase (TK) gene fused to the promoter-regulatory domains of late ( γ 2) genes were regulated as bonafide γ 2 genes when resident in the herpes simplex virus 1 genome but could not be differentiated from β genes when introduced by transfection and stably integrated into the environment of the host genome ( S. Silver and B. Roizman, Mol. Cell. Biol., 5, 518–528, 1985 ). We report here that β-TK and the chimeric γ 2-TK gene transfected into TK − baby hamster kidney (BHKtk −) were induced by α4 and α0 but not by the other α genes. Specifically: (i) Both TK genes were induced by cotransfection with DNA fragments carrying an intact α4 or an intact α0 gene, but not by fragments carrying only the promoter-regulatory domain or the structural sequences of the α4 gene or intact α22, α27, and α47 genes. (ii) An α4 gene carrying a 2700-bp deletion in its 3′ coding sequence also induced both genes, although less efficiently. (iii) RNA homologous to the α4 gene recovered from the cytoplasm of cells transfected with either the intact or truncated α4 gene mapped to the bonafide site of transcription initiation of the a4 gene. RNA homologous to the chimeric TK gene extracted from the cytoplasm of cells transfected with both γ 2-TK and the α4 gene was transcribed from the bonafide γ 2 gene capping site fused to the TK gene. These results indicate that the α4 gene and the α0 gene are each capable of inducing the expression of both β and γ 2 genes resident in the environment of the cellular genome, that the active site responsible for induction is located near the N terminus of the α4 protein, and reinforce the conclusion that γ 2 genes resident in the environment of the host cell cannot be used to identify the authentic determinants of γ 2 gene regulation by currently available tests.