Rigby P W, Berg P
J Virol. 1978 Nov;28(2):475-89. doi: 10.1128/JVI.28.2.475-489.1978.
Late after infection of permissive monkey cells by simian virus 40 (SV40), large amounts of SV40 DNA (30,000 to 220,000 viral genome equivalents per cell) can be isolated with the high-molecular-weight fraction of cellular DNA. Hirai and Defendi (J. Virol.9:705-707, 1972) and Hölzel and Sokol (J. Mol. Biol. 84:423-444, 1974) suggested that this SV40 DNA is covalently integrated into the cellular DNA. However, our data indicate that the high-molecular-weight viral DNA is composed of tandem, "head-to-tail" repeats of SV40 DNA and that very little, if any, of this viral DNA is covalently joined to the cellular DNA. This was deduced from the following experimental findings. The size of the SV40 DNA associated with the high-molecular-weight cellular DNA fraction is greater than 45 kilobases, based on its electrophoretic mobility in agarose gels. In this form the SV40 DNA did not produce heteroduplex structures with a marker viral DNA (an SV40 genome with a characteristic deletion and duplication). After the high-molecular-weight DNA was digested with EcoRI or HpaII endonucleases, enzymes which cleave SV40 DNA once, more than 95% of the SV40 DNA migrated as unit-length linear molecules and, after hybridization with the marker viral DNA, the expected heteroduplex structures were easily detected. Digestion of the high-molecular-weight DNA fraction with restriction endonucleases that cleave cellular, but not SV40. DNA did not alter the electrophoretic mobility of the polymeric SV40 DNA, nor did it give rise to molecules that form heteroduplex structures with the marker viral DNA. Polymeric SV40 DNA molecules produced after coinfection by two physically distinguishable SV40 genomes contain only a single type of genome, suggesting that they arise by replication rather than by recombination. The polymeric form of SV40 DNA is highly infectious for CV-1P monolayers (6.5 X 10(4) PFU per microgram of SV40 DNA), yielding virtually exclusively normal, covalently closed circular, monomer-length DNA. Quite clearly these cells have an efficient mechanism for generating monomeric viral DNA from the SV40 DNA polymers.
猿猴空泡病毒40（SV40）感染允许性猴细胞后不久，大量的SV40 DNA（每个细胞30,000至220,000个病毒基因组当量）可与细胞DNA的高分子量部分一起分离出来。平井和德芬迪（《病毒学杂志》9:705 - 707，1972年）以及霍尔泽尔和索科尔（《分子生物学杂志》84:423 - 444，1974年）提出，这种SV40 DNA是共价整合到细胞DNA中的。然而，我们的数据表明，高分子量病毒DNA由SV40 DNA的串联“头对头”重复序列组成，并且这种病毒DNA中极少（如果有的话）与细胞DNA共价连接。这是从以下实验结果推断出来的。基于其在琼脂糖凝胶中的电泳迁移率，与高分子量细胞DNA部分相关的SV40 DNA大小大于45千碱基。以这种形式，SV40 DNA不会与标记病毒DNA（具有特征性缺失和重复的SV40基因组）产生异源双链结构。用EcoRI或HpaII内切酶消化高分子量DNA后，这两种酶会切割SV40 DNA一次，超过95%的SV40 DNA以单位长度线性分子迁移，并且在与标记病毒DNA杂交后，很容易检测到预期的异源双链结构。用能切割细胞DNA但不能切割SV40 DNA的限制性内切酶消化高分子量DNA部分，不会改变聚合型SV40 DNA的电泳迁移率，也不会产生与标记病毒DNA形成异源双链结构的分子。由两种物理上可区分的SV40基因组共同感染后产生的聚合型SV40 DNA分子仅包含单一类型的基因组，这表明它们是通过复制而非重组产生的。SV40 DNA的聚合形式对CV - 1P单层细胞具有高度感染性（每微克SV40 DNA有6.5×10⁴个空斑形成单位），几乎只产生正常的、共价闭合环状的单体长度DNA。很明显，这些细胞具有一种有效的机制，可从SV40 DNA聚合物生成单体病毒DNA。
