Wiehle W, Hecker M, Reichstein B, Mach F
Z Allg Mikrobiol. 1984;24(2):119-24.
Escherichia coli K12 strains containing the plasmid pBR322 often show varying contents of plasmid oligomers, in which the monomer units are arranged in tandem. When the concentration of the plasmid-selective antibiotic tetracycline in the medium becomes increased selection of cells containing largely higher oligomers occurs. The number of monomer units organized in the oligomers increases with tetracycline concentration. recA- mutants are unable to generate oligomers under the same conditions and show lower tetracycline resistance. This observations suggest a selective advantage of oligomer containing cells in the presence of tetracycline as a result of higher gene dosage. But E. coli cells transformed with monomers, dimers, trimers, as well as tetramers of pBR322 are characterized by roughly the same plasmid DNA content as well as plasmid coded beta-lactamase and resistance to tetracycline.
含有质粒pBR322的大肠杆菌K12菌株常常表现出不同含量的质粒寡聚体，其中单体单元呈串联排列。当培养基中质粒选择性抗生素四环素的浓度增加时，就会选择出含有更高寡聚体的细胞。寡聚体中组织的单体单元数量随四环素浓度增加。recA-突变体在相同条件下无法产生寡聚体，并且表现出较低的四环素抗性。这些观察结果表明，由于基因剂量较高，在四环素存在的情况下，含有寡聚体的细胞具有选择性优势。但是用pBR322的单体、二聚体、三聚体以及四聚体转化的大肠杆菌细胞，其质粒DNA含量、质粒编码的β-内酰胺酶以及对四环素的抗性大致相同。
