Heffron F, Rubens C, Falkow S
Proc Natl Acad Sci U S A. 1975 Sep;72(9):3623-7. doi: 10.1073/pnas.72.9.3623.
A series of recombinant plasmids was generated in Escherichia coli in which the TEM beta-lactamase translocon (TnA) was inserted into the small plasmid RSF1010. RSF1010 is a 5.5 X 10(6) dalton nonconjugative plasmid which confers resistance to streptomycin and sulfonamide. The recombinant plasmids can be classified into three clearly defined phenotypic groups. Group I is ampicillin-, streptomycin- and sulfonamide-resistant. Group II is ampicillin- and sulfonamide-resistant but has lost streptomycin resistance. Group III is ampicillin-resistant but is sensitive to sulfonamide and shows a simultaneous 30-fold reduction in the minimal inhibitory concentration of streptomycin. It was possible to map the site of insertion of TnA within RSF1010 by electron microscope studies of DNA heteroduplexes formed between RSF1010 and recombinant plasmids. Insertions of TnA occur at, at least, 12 distinct sites in a region corresponding to one-third of the RSF1010 DNA molecule. Those insertions giving rise to particular phenotypes are clustered. Insertions of TnA-like insertion sequences (IS) appear to give rise to strongly polar mutations.
在大肠杆菌中构建了一系列重组质粒，其中TEMβ-内酰胺酶转座子（TnA）被插入到小质粒RSF1010中。RSF1010是一个5.5×10⁶道尔顿的非接合性质粒，赋予对链霉素和磺胺的抗性。这些重组质粒可分为三个明确的表型组。第一组对氨苄青霉素、链霉素和磺胺具有抗性。第二组对氨苄青霉素和磺胺具有抗性，但失去了链霉素抗性。第三组对氨苄青霉素具有抗性，但对磺胺敏感，并且链霉素的最低抑菌浓度同时降低了30倍。通过对RSF1010与重组质粒之间形成的DNA异源双链体进行电子显微镜研究，有可能确定TnA在RSF1010中的插入位点。TnA的插入至少发生在对应于RSF1010 DNA分子三分之一区域的12个不同位点。那些导致特定表型的插入是成簇的。类似TnA的插入序列（IS）的插入似乎会导致强极性突变。
