Ljungquist E, Bukhari A I
Proc Natl Acad Sci U S A. 1977 Aug;74(8):3143-7. doi: 10.1073/pnas.74.8.3143.
We have compared the process of prophage lambda induction with that of prophage Mu. According to the Campbell model, rescue of lambda DNA from the host DNA involves reversal of lambda integration such that the prophage DNA is excised from the host chromosome. We have monitored this event by locating the prophage DNA with a technique in which DNA of the lysogenic cells is cleaved with a restriction endonuclease and fractionated in agarose gels. The DNA fragments are denatured in gels, transferred to a nitrocellulose paper, and hybridized with 32P-labeled mature phage DNA. The fragments containing prophage DNA become visible after autoradiography. Upon prophage lambda induction, the phage-host junction fragments disappear and the fragment containing the lambda att site appears. No such excision is seen in prophage Mu. The Mu-host junction fragments remain intact well into the lytic cycle, when Mu DNA has undergone many rounds of replication and apparently many copies of Mu DNA have been integrated into the host DNA. Therefore, we postulate that Mu DNA replicates in situ and the replication generates a form of Mu DNA active in the integrative recombination between Mu DNA and host DNA. This type of mechanism may be common to many transposable elements.
我们已将λ原噬菌体诱导过程与Mu原噬菌体的诱导过程进行了比较。根据坎贝尔模型，从宿主DNA中拯救λDNA涉及λ整合的逆转，从而使原噬菌体DNA从宿主染色体上切除。我们通过一种技术来监测这一事件，即先用限制性内切核酸酶切割溶原细胞的DNA，然后在琼脂糖凝胶中进行分级分离。DNA片段在凝胶中变性，转移到硝酸纤维素纸上，并用³²P标记的成熟噬菌体DNA进行杂交。含有原噬菌体DNA的片段在放射自显影后可见。在λ原噬菌体诱导时，噬菌体-宿主连接片段消失，含有λ附着位点的片段出现。在Mu原噬菌体中未观察到这种切除现象。Mu-宿主连接片段在裂解周期中一直保持完整，此时Mu DNA已经历了多轮复制，显然有许多拷贝的Mu DNA已整合到宿主DNA中。因此，我们推测Mu DNA在原位复制，并且这种复制产生了一种在Mu DNA与宿主DNA之间的整合重组中具有活性的Mu DNA形式。这种机制可能在许多转座元件中很常见。
