Renne R, Mergia A, Renshaw-Gegg L W, Neumann-Haefelin D, Luciw P A
Department of Medical Pathology, University of California, Davis 95616.
Virology. 1993 Jan;192(1):365-9. doi: 10.1006/viro.1993.1045.
Simian foamy virus type 3 (SFV-3) is a retrovirus that has a complex genome organization and encodes two open reading frames (ORF-1 and ORF-2) in addition to the genes coding for gag, pol, and env. In this report, we demonstrate that ORF-1 of SFV-3 encodes a transcriptional transactivator designated taf (transactivator of foamy virus) which augments gene expression directed by the viral long terminal repeat (LTR). The taf responsive elements have been mapped to the U3 region of the LTR, between positions -637 and -180 (+1 represents the transcription initiation site). Two regions between -637 and -180 in the LTR are targets for taf transactivation. These target sequences for taf confer responsiveness to a heterologous promoter independent of orientation; thus, they function like conditional enhancers. The R-U5 region of the viral LTR is shown to have an inhibitory effect on gene expression. SFV-1 is a related spumavirus and encodes a taf gene that augments expression directed by the SFV-3 LTR as well as the SFV-1 LTR; however, the taf gene of SFV-3 transactivates the SFV-3 LTR but not the SFV-1 LTR. These data on regulatory elements in the SFV-3 LTR show that the mechanism of foamy virus transactivation is significantly different from lentiviruses as well as from the HTLV group of viruses.
猿猴泡沫病毒3型（SFV-3）是一种逆转录病毒，其基因组结构复杂，除了编码gag、pol和env的基因外，还编码两个开放阅读框（ORF-1和ORF-2）。在本报告中，我们证明SFV-3的ORF-1编码一种转录反式激活因子，命名为taf（泡沫病毒反式激活因子），它可增强由病毒长末端重复序列（LTR）指导的基因表达。taf反应元件已被定位到LTR的U3区域，位于-637和-180位之间（+1代表转录起始位点）。LTR中-637和-180之间的两个区域是taf反式激活的靶点。taf的这些靶序列赋予异源启动子对其反应性，且与方向无关；因此，它们的功能类似于条件增强子。病毒LTR的R-U5区域对基因表达有抑制作用。SFV-1是一种相关的泡沫病毒，编码一个taf基因，该基因可增强由SFV-3 LTR以及SFV-1 LTR指导的表达；然而，SFV-3的taf基因可反式激活SFV-3 LTR，但不能反式激活SFV-1 LTR。这些关于SFV-3 LTR调控元件的数据表明，泡沫病毒反式激活的机制与慢病毒以及HTLV病毒组有显著不同。
