Cupelli L A, Lenz J
Department of Molecular Genetics, Albert Einstein College of Medicine, Bronx, New York 10461.
J Virol. 1991 Dec;65(12):6961-8. doi: 10.1128/JVI.65.12.6961-6968.1991.
Sequences within the R components of the long terminal repeats (LTRs) of several retroviruses are known to be involved at various steps in expression of the viral genomes. A series of experiments was performed to test whether sequences within the R regions of the murine leukemia viruses Akv and SL3-3 affect viral expression. By using plasmid clones of the viral LTRs linked to a reporter gene, deletion of the R region was found to decrease expression to variable extents in a series of mammalian cell lines, with the largest effects being detected in murine fibroblasts. R-region sequences from the human immunodeficiency virus type 1 LTR or a random sequence were unable to substitute for the murine leukemia virus sequences. Transcripts from the R-region-deleted templates were initiated at the proper site in the LTR, but their levels were decreased at least 10-fold. Nuclear run-on assays showed that the decrease caused by the R-region deletions was due, in part, to an effect on RNA polymerase loading, suggesting an effect on transcriptional initiation. The remainder of the activity was presumably due to a posttranscriptional effect. Analysis of the R-region sequences of murine leukemia viruses and related retroviruses led to the prediction of a conserved secondary structure in the transcribed RNA that might have a role in activity. We conclude that R-region sequences are of importance for the expression of a variety of retroviruses.
已知几种逆转录病毒的长末端重复序列（LTRs）的R组件中的序列在病毒基因组表达的各个步骤中发挥作用。进行了一系列实验，以测试鼠白血病病毒Akv和SL3-3的R区域内的序列是否影响病毒表达。通过使用与报告基因相连的病毒LTR的质粒克隆，发现在一系列哺乳动物细胞系中，R区域的缺失会在不同程度上降低表达，在鼠成纤维细胞中检测到的影响最大。来自人类免疫缺陷病毒1型LTR的R区域序列或随机序列无法替代鼠白血病病毒序列。来自R区域缺失模板的转录本在LTR中的正确位点起始，但其水平至少降低了10倍。核转录分析表明，R区域缺失导致的表达降低部分归因于对RNA聚合酶加载的影响，提示对转录起始有影响。其余的活性可能归因于转录后效应。对鼠白血病病毒和相关逆转录病毒的R区域序列进行分析后，预测转录RNA中存在一种保守的二级结构，可能在活性中发挥作用。我们得出结论，R区域序列对多种逆转录病毒的表达至关重要。
