Niikura M, Dodgson J B, Cheng H H
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA.
Arch Virol. 2006 Jul;151(7):1431-8. doi: 10.1007/s00705-006-0724-0. Epub 2006 Feb 20.
The Marek's disease virus (MDV) genome contains 2 sets of 132-bp tandem repeat sequences. An increase in 132-bp repeat units has been associated with attenuation of oncogenicity during in vitro passage. By cloning entire genomes, we demonstrated that the copy number of 132-bp repeats can differ within an individual MDV genome. The stability of the 132-bp repeats during cell passage depended on the initial copy number. When both sets of repeats contained 2 copies, the copy number remained stable, while if even 1 set of repeats contained 6 copies, repeat expansion occurred relatively quickly. This expansion did not affect the in vitro growth curve. However, when MDV clones with low and high copy numbers were passed together, genomes with expanded repeats rapidly predominated, mimicking the behavior of naturally-occurring MDV. These results suggest that the preponderance of high-copy repeats after passage reflects intracellular copy number within individual infected cells rather than an influence on the spread of the virus.
马立克氏病病毒（MDV）基因组包含两组132碱基对的串联重复序列。在体外传代过程中，132碱基对重复单元的增加与致癌性的减弱有关。通过克隆整个基因组，我们证明了132碱基对重复序列的拷贝数在单个MDV基因组内可能不同。132碱基对重复序列在细胞传代过程中的稳定性取决于初始拷贝数。当两组重复序列都包含2个拷贝时，拷贝数保持稳定，而如果哪怕一组重复序列包含6个拷贝，重复序列的扩增就会相对迅速地发生。这种扩增并不影响体外生长曲线。然而，当低拷贝数和高拷贝数的MDV克隆一起传代时，具有扩增重复序列的基因组迅速占主导地位，这与自然发生的MDV的行为相似。这些结果表明，传代后高拷贝重复序列的优势反映了单个感染细胞内的细胞内拷贝数，而不是对病毒传播的影响。
