Yoshike K, Defendi V
J Virol. 1977 Aug;23(2):323-37. doi: 10.1128/JVI.23.2.323-337.1977.
The possible addition of extra sequences to simian virus 40 (SV40) DNA was analyzed by electron microscopy in two different cell systems, productively infected monkey cells and activated heterokaryons on monkey and transformed mouse 3T3 cells. We found that the closed circular DNA fraction, extracted from monkey cells at 70 h after infection with nondefective SV40 at a multiplicity of infection of 6 PFU/cell, contained oversized molesules (1.1 to 2.0 fractional lengths of SV40 DNA) constituting about 8% of the molecules having lengths equal to or shorter than SV40 dinner DNA. The oversized molecules had the entired SV40 sequences. The added DNA was heterogeneous in length. The sites of addition were not specific with reference to the EcoRi site. These results suggest that recombination between monkey and SV40 DNAs or partial duplication of SV40 DNA occurs at many sites on the SV40 chromosome. The integrated SV40 DNA is excised and replicates in activated heterokaryons. In this system, besides SV40 DNA we found heterogeneous undersized and oversized molecules containing SV40 sequences in the closed circular DNA population. Additions differeing in size appeared to be overlapping and to have occurred at a preferential site on the SV40 chromosome. These results support the hypothesis that host DNA can be added to SV40 DNA at the site of integration at the time of excision.
通过电子显微镜在两种不同的细胞系统中分析了猿猴病毒40（SV40）DNA可能添加的额外序列，这两种细胞系统分别是被有效感染的猴细胞以及由猴细胞与转化的小鼠3T3细胞形成的活化异核体。我们发现，在感染复数为6个蚀斑形成单位/细胞的情况下，用无缺陷的SV40感染猴细胞70小时后提取的闭环DNA部分，包含超大分子（SV40 DNA长度的1.1至2.0倍），约占长度等于或短于SV40双链DNA的分子的8%。这些超大分子具有完整的SV40序列。添加的DNA长度各异。添加位点相对于EcoRi位点不具有特异性。这些结果表明，猴DNA与SV40 DNA之间的重组或SV40 DNA的部分重复发生在SV40染色体的多个位点上。整合的SV40 DNA在活化异核体中被切除并复制。在这个系统中，除了SV40 DNA，我们在闭环DNA群体中还发现了包含SV40序列的长度各异的较小和超大分子。大小不同的添加片段似乎相互重叠，且发生在SV40染色体的一个优先位点上。这些结果支持了这样一种假说，即在切除时宿主DNA可以在整合位点添加到SV40 DNA上。
