Smith R H, Zhao Y, O'Callaghan D J
Department of Microbiology and Immunology, Louisiana State University Medical Center, Shreveport 71130-3932.
Virology. 1994 Aug 1;202(2):760-70. doi: 10.1006/viro.1994.1398.
The equine herpesvirus type 1 (EHV-1) immediate-early (IE) gene product, an ICP4 homolog, is the major regulatory protein encoded by EHV-1 during cytolytic infection. The IE gene product has been demonstrated to induce reporter gene expression directed by both homologous and heterologous viral promoters, including the EHV-1 thymidine kinase (tk) promoter, the herpes simplex virus type 1 (HSV-1) tk and ICP4 promoters, and the simian virus 40 early promoter. In this report, the transcriptional activation domain of the EHV-1 IE gene product was mapped to within an acidic, 87-amino-acid region (amino acids 3 to 89) at the amino-terminus of the IE molecule. It is demonstrated that the IE transcriptional activation domain, when fused to the DNA-binding domain of the yeast transcriptional activator GAL4, can activate gene expression in cell lines derived from at least two different species. Moreover, it is shown that the EHV-1 IR2 gene product (Harty and O'Callaghan, J. Virol. 65, 3829-3838, 1991), a truncated form of the IE polypeptide lacking IE amino acid residues 1-322 (and, therefore lacks the deduced transcriptional activation domain), fails to transactivate the EHV-1 tk promoter, but retains the ability to down-regulate the EHV-1 IE promoter. Fusion of the acidic transcriptional activation domain of the HSV-1 virion protein VP16 to the transactivation-deficient IR2 gene product restored the ability of this truncated IE polypeptide to transactivate the EHV-1 tk promoter. These findings suggest a role for the IR2 protein as a trans-repressor of EHV-1 gene expression.
1型马疱疹病毒（EHV-1）的立即早期（IE）基因产物是一种ICP4同源物，是EHV-1在溶细胞性感染期间编码的主要调节蛋白。IE基因产物已被证明可诱导由同源和异源病毒启动子指导的报告基因表达，包括EHV-1胸苷激酶（tk）启动子、1型单纯疱疹病毒（HSV-1）的tk和ICP4启动子以及猿猴病毒40早期启动子。在本报告中，EHV-1 IE基因产物的转录激活结构域被定位到IE分子氨基末端的一个酸性的87个氨基酸区域（氨基酸3至89）内。结果表明，IE转录激活结构域与酵母转录激活因子GAL4的DNA结合结构域融合后，可在源自至少两种不同物种的细胞系中激活基因表达。此外，研究表明，EHV-1 IR2基因产物（Harty和O'Callaghan，《病毒学杂志》65，3829 - 3838，1991），即IE多肽的截短形式，缺少IE氨基酸残基1 - 322（因此缺乏推导的转录激活结构域），无法反式激活EHV-1 tk启动子，但保留了下调EHV-1 IE启动子的能力。将HSV-1病毒粒子蛋白VP16的酸性转录激活结构域与反式激活缺陷的IR2基因产物融合，恢复了这种截短的IE多肽反式激活EHV-1 tk启动子的能力。这些发现表明IR2蛋白作为EHV-1基因表达的反式抑制因子发挥作用。
