Kholodiĭ G Ia, Mindlin S Z
Genetika. 1985 May;21(5):707-15.
We studied the ability of lambda, phi 80 and their hybrid lambda att80 to lysogenize homoimmune monolysogens and examined the prophage locations on the chromosome of the resulting polylysogens. We observed an effective integration of phi 80 and lambda att80, in contrast to lambda, into the host chromosome, exclusively, at the attachment sites that were not occupied by the resident prophage (nontandem). Besides, the lambda att80 (int+) prophage was observed to ensure effective nontandem integration of a homoimmune int mutant DNA. Hence, we inferred that the expression of the int gene in the phi 80 prophage is constitutive, cI-independent and results in nontandem integration of the homoimmune prophage. The validity of this inference has been supported experimentally: (i) the only lysogen that was found to contain a phi 80 tandem was highly unstable (spontaneous segregation of monolysogens occurred 6-7 times more frequently than with the lambda tandem); (ii) an int inactivating mutation stabilized the phi 80 tandem; as a result, the int mutant has the frequency of tandem integration as high as that of lambda, while no nontandem integration was observed. A hypothesis is proposed which accounts for the instability of the phi 80 tandems and explains the relation between this phenomenon and the prophage ability to integrate into secondary attachment sites in the presence of the primary (normal) one.
我们研究了λ噬菌体、φ80噬菌体及其杂种λatt80噬菌体使同免疫单溶源菌溶源化的能力，并检查了所得多溶源菌染色体上原噬菌体的位置。我们观察到，与λ噬菌体不同，φ80噬菌体和λatt80噬菌体能有效地整合到宿主染色体上，且专门整合到未被常驻原噬菌体占据的附着位点（非串联）。此外，观察到λatt80（int+）原噬菌体可确保同免疫int突变体DNA的有效非串联整合。因此，我们推断φ80原噬菌体中int基因的表达是组成型的、不依赖cI的，并且会导致同免疫原噬菌体的非串联整合。这一推断的正确性已得到实验支持：（i）唯一被发现含有φ80串联的溶源菌非常不稳定（单溶源菌的自发分离发生频率比λ串联高6 - 7倍）；（ii）int失活突变使φ80串联稳定；结果，int突变体的串联整合频率与λ噬菌体一样高，而未观察到非串联整合。我们提出了一个假设，该假设解释了φ80串联的不稳定性，并解释了这一现象与原噬菌体在存在初级（正常）附着位点时整合到次级附着位点的能力之间的关系。
