Hull Stacey, Boris-Lawrie Kathleen
Center for Retrovirus Research, Department of Veterinary Biosciences, The Ohio State University, 1925 Coffey Road, Columbus, OH 43210-1093, USA.
J Virol. 2002 Oct;76(20):10211-8. doi: 10.1128/jvi.76.20.10211-10218.2002.
Retroviruses utilize an unspliced version of their primary transcription product as an RNA template for synthesis of viral Gag and Pol structural and enzymatic proteins. Cytoplasmic expression of the gag-pol RNA is achieved despite the lack of intron removal and the presence of a long and highly structured 5' untranslated region that inhibits efficient ribosome scanning. In this study, we have identified for the first time that the 5' long terminal repeat (LTR) of Mason-Pfizer monkey virus (MPMV) facilitates Rev/Rev-responsive element-independent expression of HIV-1 gag-pol reporter RNA. The MPMV RU5 region of the LTR is necessary and directs functional interaction with cellular posttranscriptional modulators present in human 293 and monkey COS cells but not in quail QT-6 cells and does not require any viral protein. Deletion of MPMV RU5 decreases the abundance of spliced mRNA but has little effect on cytoplasmic accumulation of unspliced gag-pol RNA despite complete elimination of detectable Gag protein production. MPMV RU5 also exerts a positive effect on the cytoplasmic expression of intronless luc RNA, and ribosomal profile analysis demonstrates that MPMV RU5 directs subcellular localization of the luc transcript to polyribosomes. Our findings have a number of similarities with those of reports on 5' terminal posttranscriptional control elements in spleen necrosis virus and human foamy virus RNA and support the model that divergent retroviruses share 5' terminal RNA elements that interact with host proteins to program retroviral RNA for productive cytoplasmic expression.
逆转录病毒利用其初级转录产物的未剪接版本作为RNA模板，用于合成病毒Gag和Pol结构蛋白及酶蛋白。尽管缺乏内含子去除，且存在一个长且高度结构化的5'非翻译区抑制有效核糖体扫描，但gag-pol RNA仍能在细胞质中表达。在本研究中，我们首次鉴定出，猴泡沫病毒（MPMV）的5'长末端重复序列（LTR）促进HIV-1 gag-pol报告RNA在不依赖Rev/Rev反应元件的情况下表达。LTR的MPMV RU5区域是必需的，并指导与人类293细胞和猴COS细胞中存在的细胞转录后调节剂进行功能相互作用，但在鹌鹑QT-6细胞中不存在这种相互作用，且不需要任何病毒蛋白。删除MPMV RU5会降低剪接mRNA的丰度，但对未剪接gag-pol RNA的细胞质积累影响不大，尽管可检测到的Gag蛋白产生完全消除。MPMV RU5对无内含子的荧光素酶（luc）RNA的细胞质表达也有积极作用，核糖体图谱分析表明，MPMV RU5将luc转录本的亚细胞定位导向多核糖体。我们的发现与关于脾坏死病毒和人泡沫病毒RNA中5'末端转录后控制元件的报道有许多相似之处，并支持这样一种模型，即不同的逆转录病毒共享5'末端RNA元件，这些元件与宿主蛋白相互作用，为逆转录病毒RNA进行有效的细胞质表达编程。
