CONTROL OF PAPILLOMAVIRUS LATE TRANSCRIPTION

乳头瘤病毒可引起鳞状细胞癌的良性和恶性病变 高等脊椎动物的上皮细胞。它们的完整的裂解循环 病毒(包括晚期基因表达)只发生在 鳞状上皮的分化细胞。恶性病变和 培养中受感染的细胞不会产生病毒。我们用的是牛 以1型乳头瘤病毒L为模型系统研究人乳头瘤病毒 乳头瘤病毒晚期基因的表达及其调控。转录的 作图数据表明，编码主要基因和 次要衣壳蛋白的表达来自一种很强的病毒转录 启动子(称为后期启动子)，仅在生产中有效 感染的上皮细胞。晚期的mRNA几乎检测不到 非生产性感染(转化)细胞。牛细小病毒1型突变株的分析 与大部分晚期区域的缺失表明BPV-1的晚期 即使在转化过程中，也可以有效地利用多聚腺苷化位点 细胞。真核表达载体也被用来证明 晚期聚(A)位点是比早期更有效的聚(A)位点 Poly(A)站点。后期Poly(A)站点的使用效率低下 位于其正常环境中，位于早期Poly(A)下游3kb 站点可能部分是由于转录终止或暂停 已被证明发生在早期和晚期的Poly(A)位点之间 转化细胞，并在后期部分转化为短抑制元件 3‘非编码区。该晚期3‘UTR元件已被显示为不起作用 先前认为的不稳定的晚期mRNAs，可能在 RNA加工或运输水平。我们还有证据表明BPV-1 Poly(A)位点的选择可能受剪接因子的调控。BPV-1晚发 启动子转录本可以在第325或3605位与受体拼接 这种剪接位置的选择在非生产性方面受到不同的调节 以及高效感染的细胞。我们已经证明，使用转染法 研究表明，这两个剪接点之间的外显子序列调节 新台币3764位的剪接供体的使用。此外，我们已经表明， 在没有这些外显子的情况下有效利用NT 3764剪接位点 序列可以抑制早期Poly(A)位点的多聚腺苷基化。

The papillomaviruses cause benign and malignant lesions of squamous epithelia in higher vertebrates. The complete lytic cycle of these viruses (including late gene expression) occurs only in the differentiated cells of the squamous epithelium. Malignant lesions and infected cells in culture do not produce virus. We have used bovine papillomavirus type 1 (BPV-l) as a model system for the study of papillomavirus late gene expression and its control. Transcriptional mapping data indicates that the late mRNAs which encode the major and minor capsid proteins are expressed from a strong viral transcriptional promoter (called the late promoter) which is active only in productively infected epithelium. Late mRNAs are almost undetectable in nonproductively infected (transformed) cells. Analysis of BPV-1 mutants with deletion of most of the late region demonstrated that the BPV-1 late polyadenylation site can be efficiently utilized even in transformed cells. Eukaryotic expression vectors have also been used to show that the late poly(A) site is a more efficient poly(A) site than the early poly(A) site. The inefficient use of the late poly(A) site when it is positioned in its normal context 3 kb downstream of the early poly(A) site may be due partially to transcription termination or pausing which has been shown to occur between the early and late poly(A) sites in transformed cells and partially to a short inhibitory element in the late 3'UTR. This late 3'UTR element has been shown not to function by destabilizing late mRNAs as was previously thought and may function at an RNA processing or transport level. We also have evidence that BPV-1 poly(A) site choice could be regulated by splicing factors. BPV-1 late promoter transcripts can be spliced into acceptors at nt 3225 or 3605 and this splice site choice is differentially regulated in nonproductively and productively infected cells. We have shown, using transfection studies, that exon sequences between these two splice sites modulate the use of the splice donor at nt 3764. In addition, we have shown that efficient use of the nt 3764 splice site in the absence of these exon sequences can suppress polyadenylation at the early poly(A) site.