Cook W J, Wobbe K K, Böni J, Coen D M
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, 02115, USA.
Virology. 1996 Apr 1;218(1):193-203. doi: 10.1006/viro.1996.0179.
The herpes simplex virus type 1 thymidine kinase (tk) gene (UL23) lies upstream of the gH (UL22) gene with its 3' end overlapping the gH promoter, and it overlaps the UL24 gene's regulatory and coding sequences at its 5' end in a head-to-head orientation. Thus, tk expression could affect gH expression by promoter occlusion and UL24 expression by transcriptional or posttranscriptional mechanisms. To investigate these possibilities, we analyzed the effects of tk promoter mutations that reduce tk expression on gH and UL24 expression. For gH, tk promoter mutations did not increase the accumulation of gH mRNA or the rate of gH transcription. Thus, tk expression does not appear to down-regulate gH expression. In contrast, we found that decreased tk expression correlated with increased accumulation of UL24 mRNA, particularly a 1.4-kb transcript, at early times postinfection during peak expression of tk, but not at late times when tk mRNA levels have fallen. Results from viral co-infection experiments indicated that down-regulation of UL24 mRNA accumulation requires tk expression in cis. Nuclear run-off experiments did not detect differences in UL24 transcription rates in the mutant viruses. Although we cannot completely exclude a transcriptional mechanism for this down-regulation, these results can be explained by an antisense RNA mechanism acting preferentially in cis.
单纯疱疹病毒1型胸苷激酶（tk）基因（UL23）位于gH（UL22）基因上游，其3'端与gH启动子重叠，且其5'端以头对头方向与UL24基因的调控序列和编码序列重叠。因此，tk表达可能通过启动子封闭影响gH表达，并通过转录或转录后机制影响UL24表达。为了研究这些可能性，我们分析了降低tk表达的tk启动子突变对gH和UL24表达的影响。对于gH，tk启动子突变并未增加gH mRNA的积累或gH转录速率。因此，tk表达似乎不会下调gH表达。相反，我们发现tk表达降低与感染后早期（在tk表达高峰期）UL24 mRNA的积累增加相关，特别是一种1.4 kb的转录本，但在tk mRNA水平下降的后期则不然。病毒共感染实验结果表明，UL24 mRNA积累的下调需要tk顺式表达。核转录实验未检测到突变病毒中UL24转录速率的差异。虽然我们不能完全排除这种下调的转录机制，但这些结果可以通过优先顺式作用的反义RNA机制来解释。
