Anderson K P, Low M A, Lie Y S, Keller G A, Dinowitz M
Department of Medicinal and Analytical Chemistry, Genentech, Inc., South San Francisco, California 94080.
Virology. 1991 Mar;181(1):305-11. doi: 10.1016/0042-6822(91)90496-x.
The presence of budding C-type and intracytoplasmic A-type particles in Chinese hamster ovary (CHO) cells is well documented. However, extensive screening has failed to detect any evidence of infectivity. Continuous-flow ultracentrifugation has been used to concentrate extracellular particles from culture fluid of a recombinant CHO cell subclone for molecular characterization. Particles exhibiting reverse transcriptase activity and associated with mammalian C-type retrovirus structural proteins banded in sucrose gradients at a density characteristic of retroviruses. Examination of gradient-purified particles by electron microscopy revealed morphology and size similar to other retroviruses. Double-gradient-purified particles contained RNA which hybridized to probes for murine leukemia virus, and endogenous Chinese hamster intracisternal A-particle elements. DNA sequence analysis of a cDNA clone isolated from purified particles revealed multiple interruptions of the endonuclease reading frame, providing one possible explanation for the noninfectious nature of the observed particles. Sequences present as RNA in purified particles were also present as conserved, repetitive, provirus sequences in genomic DNA of all CHO cell lines examined and in Chinese hamster liver DNA. The observed particles are therefore likely to be the products of endogenous retroviruslike elements present in the germline of Chinese hamsters.
中国仓鼠卵巢（CHO）细胞中存在芽生的C型和胞质内A型颗粒，这一点已有充分记录。然而，广泛的筛选未能检测到任何感染性证据。连续流超速离心已被用于从重组CHO细胞亚克隆的培养液中浓缩细胞外颗粒，以进行分子表征。表现出逆转录酶活性并与哺乳动物C型逆转录病毒结构蛋白相关的颗粒，在蔗糖梯度中以逆转录病毒特有的密度形成条带。通过电子显微镜检查梯度纯化的颗粒，发现其形态和大小与其他逆转录病毒相似。双梯度纯化的颗粒含有与鼠白血病病毒探针以及内源性中国仓鼠脑内A颗粒元件杂交的RNA。从纯化颗粒中分离出的一个cDNA克隆的DNA序列分析显示，核酸内切酶阅读框存在多处中断，这为观察到的颗粒的非感染性本质提供了一种可能的解释。在纯化颗粒中以RNA形式存在的序列，在所有检测的CHO细胞系的基因组DNA以及中国仓鼠肝脏DNA中也以保守的、重复的前病毒序列形式存在。因此，观察到的颗粒很可能是中国仓鼠种系中存在的内源性逆转录病毒样元件的产物。
