Yale University Medical School, 333 Cedar Street, New Haven, CT 06510, USA.
J Neurovirol. 2011 Apr;17(2):131-45. doi: 10.1007/s13365-010-0007-0. Epub 2010 Dec 7.
In transmissible encephalopathies (TSEs), it is commonly believed that the host prion protein transforms itself into an infectious form that encodes the many distinct TSE agent strains without any nucleic acid. Using a Ф29 polymerase and chromatography strategy, highly infectious culture and brain preparations of three different geographic TSE agents all contained novel circular DNAs. Two circular "Sphinx" sequences, of 1.8 and 2.4 kb, copurified with infectious particles in sucrose gradients and, as many protected viruses, resisted nuclease digestion. Each contained a replicase ORF related to microviridae that infect commensal Acinetobacter. Infectious gradient fractions also contained nuclease-resistant 16 kb mitochondrial DNAs and analysis of >4,000 nt demonstrated a 100% identity with their species-specific sequences. This confirmed the fidelity of the newly identified sequences detailed here. Conserved replicase regions within the two Sphinx DNAs were ultimately detected by PCR in cytoplasmic preparations from normal cells and brain but were 2,500-fold less than in parallel-infected samples. No trace of the two Sphinx replicases was found in enzymes, detergents, or other preparative materials using exhaustive PCR cycles. The Sphinx sequences uncovered here could have a role in TSE infections despite their apparently symbiotic, low-level persistence in normal cells and tissues. These, as well as other cryptic circular DNAs, may cause or contribute to neurodegeneration and infection-associated tumor transformation. The current results also raise the intriguing possibility that mammals may incorporate more of the prokaryotic world in their cytoplasm than previously recognized.
在传染性脑病（TSE）中，人们普遍认为宿主朊蛋白会自我转化为一种具有感染力的形式，这种形式无需任何核酸就能编码多种不同的 TSE 病原体株。利用 Ф29 聚合酶和色谱策略，三种不同地理来源的 TSE 病原体的高度传染性培养物和脑组织均含有新型环状 DNA。两种环状“狮身人面像”序列，大小分别为 1.8 和 2.4kb，与蔗糖梯度中的感染性颗粒共纯化，并且像许多受保护的病毒一样，抵抗核酸酶消化。每个序列都包含一个与感染共生菌不动杆菌的微小病毒科相关的复制酶 ORF。传染性梯度部分还含有抵抗核酸酶的 16kb 线粒体 DNA，对>4000nt 的分析表明与它们特定物种的序列完全一致。这证实了这里详细描述的新鉴定序列的准确性。在细胞质制剂和脑组织中，通过 PCR 最终在正常细胞和脑组织中检测到两种 Sphinx DNA 中的保守复制酶区域，但与平行感染的样本相比，其含量低 2500 倍。使用详尽的 PCR 循环，在酶、洗涤剂或其他制备材料中均未发现两种 Sphinx 复制酶的痕迹。尽管 Sphinx 序列在正常细胞和组织中似乎处于共生、低水平持续存在，但它们仍可能在 TSE 感染中发挥作用。这些以及其他隐匿性环状 DNA，可能导致或促成神经退行性变和感染相关的肿瘤转化。目前的结果还提出了一个有趣的可能性，即哺乳动物在其细胞质中可能整合了更多的原核世界，超出了之前的认识。
