Stoltzfus C M, Chang L J, Cripe T P, Turek L P
Department of Microbiology, University of Iowa, Iowa City.
J Virol. 1987 Nov;61(11):3401-9. doi: 10.1128/JVI.61.11.3401-3409.1987.
A region in addition to and outside the long terminal repeats (LTRs) in the gag gene of the Prague A strain of Rous sarcoma virus was found to be essential in cis for efficient cell transformation by cloned viral DNA. Transformation in chicken embryo fibroblasts, which requires infectious virus production and reinfection, was facilitated in cis by sequences between nucleotides 630 and 1659. Efficient transformation of NIH 3T3 cells in which secondary spread of virus is not necessary (as it is in chicken embryo fibroblasts) required sequences between nucleotides 630 and 1149. A src cDNA clone which also lacks this region demonstrated low transformation efficiency, indicating that the role of the cis element cannot be attributed to interference with RNA splicing. The gag gene segment required in cis for transformation, between nucleotides 630 and 1149, could substitute for the simian virus 40 enhancer in either orientation, and cells transfected with Rous sarcoma virus LTR-driven plasmids containing the gag cis element had a two- to threefold increase in steady-state viral RNA levels compared with plasmids lacking this region. Thus, additional cis-acting regulatory elements located outside the viral LTRs may modulate viral gene expression and contribute to the efficiency of cell transformation.
在劳氏肉瘤病毒布拉格A株的gag基因中，除长末端重复序列（LTRs）之外且在其外侧的一个区域被发现对于克隆的病毒DNA高效顺式细胞转化至关重要。在鸡胚成纤维细胞中进行的转化（这需要产生感染性病毒并再次感染）在顺式作用下由核苷酸630至1659之间的序列促进。在NIH 3T3细胞（其中病毒的二次传播并非必需，如同在鸡胚成纤维细胞中那样）中的高效转化需要核苷酸630至1149之间的序列。一个同样缺少该区域的src cDNA克隆显示出低转化效率，这表明顺式元件的作用不能归因于对RNA剪接的干扰。对于转化而言在顺式作用下所需的gag基因片段（在核苷酸630至1149之间）可以以任何方向替代猴病毒40增强子，并且与缺少该区域的质粒相比，用含有gag顺式元件的劳氏肉瘤病毒LTR驱动质粒转染的细胞在稳态病毒RNA水平上有两到三倍的增加。因此，位于病毒LTRs之外的额外顺式作用调控元件可能调节病毒基因表达并有助于细胞转化的效率。
