Cohen J C, Shank P R, Morris V L, Cardiff R, Varmus H E
Cell. 1979 Feb;16(2):333-45. doi: 10.1016/0092-8674(79)90010-2.
We have used restriction endonucleases which cleave the DNA of mouse mammary tumor virus (MMTV) at one site (Eco RI) and several sites (Pst I, Sac I and Bam HI) to study infection and mammary tumorigenesis in mice. Proviruses acquired during infection of BALB/c mice foster-nursed by virus-producing C3H females can be distinguished from the MMTV proviruses endogenous to uninfected BALB/c mice by the nature of the fragments generated with Pst I and Bam HI. Using this assay, we show that lactating mammary glands as well as mammary tumors from BALB/cfC3H mice have acquired MMTV DNA, and that a minimum of approximately 10% of normal glandular cells can be infected. The new proviruses appear to be linked to cellular DNA of mammary tumors and infected lactating mammary glands within a limited region (0.2 x 10(6) daltons) of the viral DNA; the location of this region, based upon mapping studies with unintegrated MMTV DNA, suggests that the orientation of these proviruses is colinear with linear DNA synthesized in infected cells and thus approximately colinear with the viral RNA. Comparisons of many mammary tumors and studies of lactating mammary glands with a high proportion of independently infected cells indicate that a large number of sites in the cellular genome can accommodate a new provirus; the acquired proviruses are rarely, if ever, found in tandem with each other or with endogenous proviruses. We cannot, however, distinguish between random integration and integration into a large number of preferred sites in the host genome. Since Eco RI and Bam HI cleavage of DNA from each mammary tumor generates a unique set of viral-specific fragments, we propose that the tumors are composed principally of cells derived from a subset of the many infected cells in a mammary gland; this proposal is supported by our finding that Eco RI digestion of DNA from several transplants of a primary tumor yields the pattern characteristic of the primary tumor.
我们使用了能在一个位点（Eco RI）和多个位点（Pst I、Sac I和Bam HI）切割小鼠乳腺肿瘤病毒（MMTV）DNA的限制性内切酶，来研究小鼠的感染和乳腺肿瘤发生。由产病毒的C3H雌性代乳喂养的BALB/c小鼠在感染期间获得的前病毒，可通过用Pst I和Bam HI产生的片段的性质，与未感染的BALB/c小鼠内源性的MMTV前病毒区分开来。通过该检测方法，我们发现BALB/cfC3H小鼠的泌乳乳腺以及乳腺肿瘤都已获得MMTV DNA，并且至少约10%的正常腺细胞可被感染。新的前病毒似乎与乳腺肿瘤的细胞DNA以及感染的泌乳乳腺中的细胞DNA在病毒DNA的有限区域（0.2×10⁶道尔顿）内相连；基于对未整合的MMTV DNA的图谱研究，该区域的位置表明这些前病毒的方向与感染细胞中合成的线性DNA共线，因此与病毒RNA大致共线。对许多乳腺肿瘤的比较以及对具有高比例独立感染细胞的泌乳乳腺的研究表明，细胞基因组中的大量位点可容纳新的前病毒；获得的前病毒很少（如果有的话）彼此串联或与内源性前病毒串联存在。然而，我们无法区分随机整合和整合到宿主基因组中的大量优先位点。由于来自每个乳腺肿瘤的DNA经Eco RI和Bam HI切割会产生一组独特的病毒特异性片段，我们提出肿瘤主要由源自乳腺中许多感染细胞子集的细胞组成；我们的这一观点得到了以下发现的支持，即对原发性肿瘤的几次移植的DNA进行Eco RI消化会产生原发性肿瘤的特征性图谱。
