Cohen S N, Miller C A
Proc Natl Acad Sci U S A. 1970 Oct;67(2):510-6. doi: 10.1073/pnas.67.2.510.
A covalently-closed circular DNA species, banding at a buoyant density of rho = 1.709 g/cm(3) in CsCl, has been identified in antibiotic-sensitive colonies of E. coli strain AB2463 (rec A(-)) after mating with a Proteus mirabilis strain that carries the R-factor, R1. This plasmid, which represents a stable segregant of R1 that has lost all of the drug resistance determinants present on the parent R-factor but which has retained its ability to be transferred by conjugation, fulfills the functional definition of the R-factor transfer unit (RTF).
在大肠杆菌AB2463菌株(rec A(-))的抗生素敏感菌落中,与携带R因子R1的奇异变形杆菌菌株交配后,鉴定出一种共价闭合环状DNA物种,其在CsCl中的浮力密度为ρ = 1.709 g/cm³。该质粒是R1的稳定分离物,它失去了亲本R因子上存在的所有耐药决定簇,但保留了通过接合转移的能力,符合R因子转移单位(RTF)的功能定义。