Structure of viral DNA and RNA in mammalian cells infected with avian sarcoma virus.
Structure of viral DNA and RNA in mammalian cells infected with avian sarcoma virus.
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感染禽肉瘤病毒的哺乳动物细胞中病毒 DNA 和 RNA 的结构。
DOI：
10.1016/0022-2836(80)90218-1
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发表时间：
1980
影响因子：
5.6
通讯作者：
Bishop,JM
中科院分区：
文献类型：
--
作者：
Quintrell,N;Hughes,SH;Varmus,HE;Bishop,JM
逆转录病毒基因的表达因宿主的不同而不同，可能受细胞机制的调节。因此，被禽肉瘤病毒（ASV）感染的禽成纤维细胞产生病毒并获得肿瘤表型，而被ASV感染的哺乳动物细胞产生很少或不产生病毒并且仅很少变成肿瘤。我们通过分析ASV感染的几种哺乳动物细胞系中的病毒DNA和RNA，探索了这些变异的起源。我们的工作是由最近开发的技术，允许分馏，检测和表征极少量的病毒核酸。每一行ASV感染的哺乳动物细胞含有一个或两个拷贝的ASV前病毒。然而，在这些细胞中产生的稳定病毒RNA的量在至少100倍的范围内变化。ASV的gag、pol、envandsrc基因在鸡胚细胞中通过3种信使RNA（gag/pol，Mr3.3 × 106; env，Mr1.8 × 106; src，Mr1.1 × 106）表达。在ASV转化的哺乳动物细胞中发现了相同的病毒mRNA，尽管三种病毒的相对量不同; gag/polmRNA在允许细胞中占主导地位，thesrc，mRNA在哺乳动物细胞中占主导地位。通过证明rcmRNA显然含有由两个不同元件组成的5′非翻译区，对这些RNA的先前描述进行了修订：从病毒基因组5′末端转座的核苷酸序列，以及与病毒基因组中的sr 5′边界相邻的核苷酸序列。我们发现了几种新的病毒mRNA形式：在同一克隆细胞中有两种独特的rcmRNA;一种比通常大得多的envRNA;两种似乎由ASV前病毒和邻近细胞DNA的最右端编码的mRNA。当病毒从哺乳动物细胞中被拯救出来并在允许的细胞中繁殖时，第一种异常持续存在，而第二种和第三种异常在被拯救的病毒复制过程中并不明显。在ASV感染的仓鼠细胞中，病毒基因表达减弱，从转化的表型恢复到正常的表型：特别是，srcmRNA的量减少了近100倍。回复突变体细胞和它们的转化的兄弟细胞含有单个相同的前病毒，位于宿主基因组内明显相同的位点。因此，病毒基因表达的变化，伴随并可能导致逆转，是不是由于无论是易位的原病毒或独立的起源的细胞line.We的结论，酶机制的ASV mRNA的起源广泛分布在脊椎动物：特别是，不同的宿主细胞可能利用相同的信号在ASV基因组内的剪接和多腺苷酸化的病毒RNA：即使是异常信号也可以在广泛的系统发育范围内得到相同的解释。然而，这些机制的调节因细胞而异，并且在转化细胞的单个克隆内病毒RNA的成熟中可能发生一致的差异。在至少一些情况下，转录可以在ASV前病毒内起始，但不间断地继续进入相邻的细胞DNA;因此，仅仅将病毒DNA插入宿主基因组中就可能诱导先前沉默的细胞基因的表达。宿主细胞对病毒基因表达的减弱可导致细胞从转化表型逆转为正常表型。我们的数据表明，宿主主要通过调节病毒的产生来调节ASV基因的表达。
The expression of retrovirus genes varies from one species of host to another and is probably regulated by cellular mechanisms. Thus, avian fibroblasts infected with avian sarcoma virus (ASV) produce virus and acquire a neoplastic phenotype, whereas ASV-infected mammalian (cells produce little or no virus and only rarely become neoplastic. We have explored the origins of these variations by analysing the viral DNA and RNA in several lines of mammalian cells infected by ASV. Our work was facilitated by recently developed techniques that permit the fractionation, detection and characterization of extremely small quantities of viral nucleic acids.Each line of ASV-infected mammalian cells contained either one or two copies of ASV provirus. Nevertheless, the amounts of stable viral RNA produced in these cells varied over a range of at least 100-fold. In permissive chicken cells, the four genes of ASV (gag,pol,envandsrc) appear to be expressed by means of three viral messenger RNAs (gag/pol,Mr3.3 × 106;env,Mr1.8 × 106; andsrc,Mr1.1 × 106). The same viral mRNAs were found in ASV-transformed mammalian cells, although the relative amounts of the three species were different; thegag/polmRNA predominated in permissive cells, thesrc, mRNA in mammalian cells. The previous description of these RNAs was revised by demonstrating that thesrcmRNA apparently contains a 5′ untranslated region composed of two distinct elements: a nucleotide sequence transposed from the 5′ end of the viral genome, and a nucleotide sequence contiguous to the 5′ boundary ofsrcin the viral genome. We encountered several novel forms of viral mRNA: two distinctivesrcmRNAs in the same clone of cells; anenvRNA appreciably larger than usual; and two mRNAs that appear to be encoded by the extreme right-hand end of the ASV provirus and adjacent cellular DNA. The first of these anomalies persisted when virus was rescued from the mammalian cells and then propagated in permissive cells, whereas the second and third anomalies were not apparent during the replication of rescued virus.Viral gene expression was attenuated in ASV-infected hamster cells that had reverted from a transformed to a normal phenotype: in particular, the amount ofsrcmRNA was reduced by almost 100-fold. The revertant cells and their transformed siblings contained single identical proviruses located at apparently identical sites within the host genome. Thus, the change in viral gene expression that accompanies and perhaps causes reversion is not due to either translocation of the provirus or independent origins of the cell lines.We conclude that the enzymatic mechanisms for the genesis of ASV mRNAs are widely distributed among vertebrates: in particular, phylogenetically disparate host cells may utilize the same signals within the ASV genome for the splicing and polyadenylation of viral RNA: even anomalous signals can be interpreted identically across a broad phylogenetic range. However, the regulation of these mechanisms varies from one cell to another, and consistent differences may occur in the maturation of viral RNA within individual clones of transformed cells. In at least some instances, transcription may be initiated within the ASV provirus but continue uninterrupted into adjacent cellular DNA; thus, the mere insertion of viral DNA into the host genome might induce the expression of previously silent cellular genes. Attenuation of viral gene expression by the host cell can lead to reversion of the cell from a transformed to a normal phenotype. Our data indicate that the host modulates ASV gene expression principally by regulating the production of viral …