Vapnek D, Alton N K, Bassett C L, Kushner S R
Proc Natl Acad Sci U S A. 1976 Oct;73(10):3492-6. doi: 10.1073/pnas.73.10.3492.
Endo-R-HindIII restriction endonuclease fragments obtained from F30 and pMB9 plasmid DNAs were ligated in vitro and used to transform a recB21 recC22 sbcB15 strain of E. coli K-12. The inability of this strain to stably maintain pMB9 alone permitted the isolation of transformants that carried hybrid plasmids containing the sbcB+ allele. These transformants became sensitive to ultraviolet light and recombination defieient and showed a 25-fold increase in the level of exonuclease I activity. The stability of the sbcB hybrid plasmids and their effects on exonuclease I activity have also been determined in wild-type and recA1 genetic backgrounds. The presence of the plasmids results in a 7-fold increase in the level of exonuclease I in a wild-type strain and 15-fold increase in a recA1 strain. The increased activity in the recA1 mutant appears to be a result of increased plasmid stability in this genetic background.
从F30和pMB9质粒DNA获得的内切R-HindIII限制性内切酶片段在体外进行连接，并用于转化大肠杆菌K-12的recB21 recC22 sbcB15菌株。该菌株无法单独稳定维持pMB9，这使得能够分离出携带含有sbcB +等位基因的杂交质粒的转化体。这些转化体对紫外线敏感且重组缺陷，并且核酸外切酶I活性水平增加了25倍。还在野生型和recA1遗传背景中确定了sbcB杂交质粒的稳定性及其对核酸外切酶I活性的影响。质粒的存在导致野生型菌株中核酸外切酶I水平增加7倍，recA1菌株中增加15倍。recA1突变体中活性的增加似乎是该遗传背景中质粒稳定性增加的结果。
