Derse D
Section of Genetics, National Cancer Institute, Frederick, Maryland 21701-1013.
J Virol. 1988 Apr;62(4):1115-9. doi: 10.1128/JVI.62.4.1115-1119.1988.
Bovine leukemia virus (BLV) and the human T-cell leukemia virus types I and II comprise a unique retrovirus subfamily which has evolved complex strategies for the regulation of gene expression. A transcriptional control circuit has been characterized in both human and bovine systems in which cis-acting promoter control elements are responsive to trans-acting factors encoded in the pX region of the virus. The BLV pX mRNA encoding the transcriptional trans-acting factor is translated in an alternate reading frame to produce an 18-kilodalton nuclear phosphoprotein, p18. A function for this protein was revealed in cotransfection experiments using mutated BLV proviruses in combination with pX expression plasmids. These experiments indicated that p18 was required for the accumulation of viral mRNAs representing full-length (genomic) and single-spliced (env) transcripts. In contrast, synthesis of the double-spliced pX mRNA was not influenced by p18 expression. Large regional deletions and substitutions of provirus sequences localized elements essential for p18 regulation to the 3' long terminal repeat. Furthermore, sequences within a 250-nucleotide region between the AATAAA signal and poly(A) site were found to be essential for efficient virus mRNA 3'-end processing and response to p18 regulation.
牛白血病病毒（BLV）以及人类T细胞白血病病毒I型和II型构成了一个独特的逆转录病毒亚科，该亚科已经进化出了复杂的基因表达调控策略。在人类和牛的系统中都已经鉴定出了一种转录控制回路，其中顺式作用启动子控制元件对病毒pX区域编码的反式作用因子有反应。编码转录反式作用因子的BLV pX mRNA在一个交替阅读框中进行翻译，产生一种18千道尔顿的核磷蛋白，即p18。在使用突变的BLV前病毒与pX表达质粒进行共转染实验中，揭示了这种蛋白质的一种功能。这些实验表明，p18是全长（基因组）和单剪接（env）转录本的病毒mRNA积累所必需的。相比之下，双剪接的pX mRNA的合成不受p18表达的影响。前病毒序列的大片段区域缺失和替换将p18调控所必需的元件定位到3'长末端重复序列。此外，发现在AATAAA信号和多聚腺苷酸位点之间的一个250个核苷酸区域内的序列对于有效的病毒mRNA 3'末端加工和对p18调控的反应是必不可少的。
