Regulation of glycoprotein D synthesis of herpes simplex virus 1 by α 4 protein, the major regulatory protein of the virus, in stably transformed cell lines: effect of the relative gene copy numbers

Summary

Earlier studies concerning γ 1 gene regulation by the α 4 protein, the major regulatory protein of herpes simplex virus 1 (HSV-1), in stably transformed cell lines, reported conflicting results, i.e., α 4 protein positively regulated the γ₁ gB gene in α 4/gB cells, while it negatively regulated the γ₁ gD gene in α 4/BJ cells. Both cell lines were derived from a common parental cell line α 4/c 113 that contains 1 copy of the α 4 gene, and the only apparent difference between them was the relative copy number of the gB and gD sequences (1 and 30–50, respectively) resident in the cell genome. We investigated this disparity by constructing a cell line (BA 4) that contains one copy each of the α 4 and γ₁ gD sequences, by fusion of α 4/c 113 and BJt cells, containing and expressing respectively 1 copy of the α 4 and gD genes. BA 4 cells constitutively expressed both the α 4, gD genes inherited from the parental cell lines (α 4/c 113 and BJt). In BA 4 cells the α 4 protein positively regulates the gD gene as evidenced from (i) higher levels of gD expression than the parental BJt cells lacking the α 4 gene, and (ii) significant decrease in gD expression under conditions that render the α 4 protein produced in BA 4 cells non-functional. In addition the γ₂gG gene contained within the DNA fragment encoding the gD gene, is also expressed in BA 4 cells. On the basis of these data, we propose that γ gene regulation by the α 4 protein is affected by the relative copy number of these genes, resident in the cell genome.