D'Agostino D M, Ciminale V, Zotti L, Chieco-Bianchi L
Department of Oncology and Surgical Sciences, University of Padova, Italy.
AIDS Res Hum Retroviruses. 1999 Oct 10;15(15):1351-63. doi: 10.1089/088922299310061.
Expression of the incompletely spliced HTLV-I mRNAs relies on the viral posttranscriptional activator Rex, whose interaction with the Rex-responsive element (RXRE) overcomes effects of cis-acting repressive sequences (CRSs). Studies based on heterologous reporter plasmids identified an intronic CRS in the 5' LTR and a CRS that overlaps with the RXRE. The present study investigated the effects of these elements in the context of spliced viral mRNAs encoding p21Rex (mRNA 1-3), Tax/Rex (mRNA 1-2-3), and Tof (mRNA 1-2-B). All three mRNAs were inefficiently expressed when transcribed in their mature intronless form, with the p21Rex mRNA showing the weakest expression. In contrast, efficient expression of p21Rex was obtained from a plasmid containing the 5' LTR and 3' portion of the genome that encoded a spliceable RNA. The defective expression of the intronless mRNAs reflected the inhibitory activity of the RXRE and the lack of 5' intronic sequences. Insertion of an intronic 5' LTR segment located upstream of the 5' CRS overcame Rex dependence conferred by the RXRE. The activity of this segment was mapped to the major splice donor and sequences overlapping with, but functionally distinct from, a previously described transcriptional enhancer. The three mRNAs responded differently to Rex and to insertion of the constitutive transport element of simian retrovirus type 1. Taken together, these results suggest that expression of the spliced mRNAs is controlled by the relative influence of positive and negative sequences present on the primary transcript as well as the Rex-RXRE interaction.
不完全剪接的HTLV-I mRNA的表达依赖于病毒转录后激活因子Rex，它与Rex反应元件（RXRE）的相互作用克服了顺式作用抑制序列（CRS）的影响。基于异源报告质粒的研究在5' LTR中鉴定出一个内含子CRS和一个与RXRE重叠的CRS。本研究调查了这些元件在编码p21Rex（mRNA 1-3）、Tax/Rex（mRNA 1-2-3）和Tof（mRNA 1-2-B）的剪接病毒mRNA背景下的作用。当以其成熟的无内含子形式转录时，所有三种mRNA的表达效率都很低，其中p21Rex mRNA的表达最弱。相比之下，从含有5' LTR和基因组3'部分的质粒中获得了p21Rex的高效表达，该质粒编码一种可剪接的RNA。无内含子mRNA的缺陷表达反映了RXRE的抑制活性和缺乏5'内含子序列。在5' CRS上游插入一个内含子5' LTR片段克服了RXRE赋予的Rex依赖性。该片段的活性定位于主要剪接供体以及与先前描述的转录增强子重叠但功能不同的序列。这三种mRNA对Rex和猴逆转录病毒1型组成型转运元件的插入反应不同。综上所述，这些结果表明剪接mRNA的表达受初级转录本上正负序列的相对影响以及Rex-RXRE相互作用的控制。
