Campbell B A, Villarreal L P
Department of Molecular Biology and Biochemistry, University of California, Irvine 92717.
Mol Cell Biol. 1988 May;8(5):1993-2004. doi: 10.1128/mcb.8.5.1993-2004.1988.
Polyomavirus (Py) enhancer core elements were compared for their ability to activate Py early transcription and DNA replication in mouse 3T6 cells, lymphoid cell lines, and undifferentiated embryonal carcinoma cells. By examining the pattern of genetic change in a number of cell-specific Py variants, we identified subenhancer sequences that may be functionally important for virus replication. Four such distinct enhancer consensus sequences were synthesized and designated as the A core (homologous with adenovirus 5 E1A enhancer), B core (homologous to the simian virus 40 A enhancer core), C core (containing an inverted repeat within the Py B enhancer), and BPV core (homologous to the bovine papillomavirus enhancer). When used to replace the complete Py B enhancer, single copies of all but the BPV element were able to fully activate Py DNA replication after transfection, but this activation was usually cell type specific. In the PCC4 embryonal carcinoma cells, only the A-core sequence was able to activate transcription and DNA replication. The BPV core sequence containing the Py F441 point change was unable to activate DNA replication in the F9 embryonal carcinoma or any other cell line. No single insertion element was dominant nor did these elements display the wild-type enhancer pattern of cell-specific activation of DNA replication. In addition, differential effects were often observed on the activation of transcription versus DNA replication. In 3T6 cells, transcription could be highly activated by the A core without a corresponding activation of DNA replication. In murine T lymphoid cell lines, the B core activated DNA replication without a corresponding increase in transcription. Furthermore, both DNA replication and, to a lesser degree, transcription often showed a strong tissue-specific dependence on the polarity of the inserted core element for activation.
对多瘤病毒（Py）增强子核心元件在小鼠3T6细胞、淋巴细胞系和未分化胚胎癌细胞中激活Py早期转录和DNA复制的能力进行了比较。通过检查一些细胞特异性Py变体的基因变化模式，我们确定了可能对病毒复制具有重要功能的亚增强子序列。合成了四个这样不同的增强子共有序列，并将其命名为A核心（与腺病毒5 E1A增强子同源）、B核心（与猴病毒40 A增强子核心同源）、C核心（在Py B增强子内含有一个反向重复序列）和BPV核心（与牛乳头瘤病毒增强子同源）。当用于取代完整的Py B增强子时，除BPV元件外，所有元件的单拷贝在转染后都能够完全激活Py DNA复制，但这种激活通常具有细胞类型特异性。在PCC4胚胎癌细胞中，只有A核心序列能够激活转录和DNA复制。含有Py F441点突变的BPV核心序列在F9胚胎癌细胞或任何其他细胞系中都无法激活DNA复制。没有单个插入元件占主导地位，这些元件也没有显示出野生型增强子的细胞特异性激活DNA复制模式。此外，在转录激活与DNA复制激活方面经常观察到不同的效应。在3T6细胞中，A核心可以高度激活转录而不相应激活DNA复制。在小鼠T淋巴细胞系中，B核心激活DNA复制而转录没有相应增加。此外，DNA复制以及在较小程度上的转录通常对插入核心元件的激活极性表现出强烈的组织特异性依赖性。
