Campbell M, Eng C, Luciw P A
Department of Medical Pathology, University of California, Davis 95616, USA.
J Virol. 1996 Oct;70(10):6847-55. doi: 10.1128/JVI.70.10.6847-6855.1996.
Simian and human foamy viruses (SFV and HFV) encode a transcriptional transactivator, Tas, which governs the levels of viral transcripts initiated by both the promoter in the long terminal repeat (LTR) and the internal promoter (IP) located within the env gene of these viruses. Tas-responsive target elements,(TRE) LTR in the LTR and (TRE) IP in the env gene, are located 5' of the TATA box in both viral promoters and function as orientation- and position-independent enhancers. We have identified a strong Tas-responsive element, designated TRE (GP), near the 3' end of the gag gene and preceding the pol gene of SFV-1. In transient-expression assays with plasmids containing reporter genes, a 59-bp DNA fragment containing TRE (GP) (nucleotides 2224 to 2282) functioned as an enhancer element, dependent on Tas, in several cell types and in the context of a heterologous basal promoter. DNase footprinting revealed that the fusion protein glutathione S-transferase-Tas, purified from genetically engineered bacteria, interacts with about 40 hp (nucleotides 2237 to 2279) in the TRE (GP). A low degree of sequence homology was noted between TRE (GP) and TRE (IP). In virus-infected cells, novel transcripts with 5' ends immediately upstream from the reverse transcriptase translation frame (nucleotides 2611 to 5778) were identified. Upstream of the start site for these transcripts is a TATA box (nucleotides 2575 to 2579), which was required for transcription in transient-expression assays. Although a spliced mRNA initiated in the viral LTR is implicated in the synthesis of the HFV Pol polyprotein which encodes protease, reverse transcriptase, and integrase, it is possible that SFV-1 contains a promoter within the pol gene for initiating a reverse transcriptase transcript. Taken together, these studies define a novel Tas-responsive enhancer element, which binds the viral transactivator, and a potential promoter within the pol gene.
猿猴泡沫病毒和人泡沫病毒（SFV和HFV）编码一种转录反式激活因子Tas，它调控由长末端重复序列（LTR）中的启动子以及这些病毒env基因内的内部启动子（IP）起始的病毒转录本水平。Tas反应性靶元件，LTR中的（TRE）LTR和env基因中的（TRE）IP，位于两个病毒启动子中TATA框的5'端，并作为方向和位置独立的增强子发挥作用。我们在SFV-1的gag基因3'端附近且在pol基因之前鉴定出一个强Tas反应性元件，命名为TRE（GP）。在使用含报告基因的质粒进行的瞬时表达试验中，一个含TRE（GP）（核苷酸2224至2282）的59 bp DNA片段在几种细胞类型中以及在异源基础启动子的背景下作为依赖于Tas的增强子元件发挥作用。DNase足迹分析显示，从基因工程细菌中纯化的谷胱甘肽S-转移酶-Tas融合蛋白与TRE（GP）中约40 hp（核苷酸2237至2279）相互作用。TRE（GP）与TRE（IP）之间存在低程度的序列同源性。在病毒感染的细胞中，鉴定出5'端紧邻逆转录酶翻译框上游（核苷酸2611至5778）的新转录本。这些转录本起始位点上游是一个TATA框（核苷酸2575至2579），其在瞬时表达试验中是转录所必需的。尽管在病毒LTR中起始的剪接mRNA与编码蛋白酶、逆转录酶和整合酶的HFV Pol多蛋白的合成有关，但SFV-1有可能在pol基因内含有一个用于起始逆转录酶转录本的启动子。这些研究共同确定了一个与病毒反式激活因子结合的新型Tas反应性增强子元件以及pol基因内的一个潜在启动子。
