Bastin M
J Gen Microbiol. 1981 Mar;123(1):187-91. doi: 10.1099/00221287-123-1-187.
The two HindIII fragments of polyoma virus DNA were cloned in the HindIII site of plasmid pBR322, a site located in the RNA polymerase promoter involved in the expression of tetracycline resistance. Although insertion of foreign DNA into this site did not always result in the complete loss of tetracycline resistance, Escherichia coli K12 strain chi 1776 harbouring recombinant plasmids exhibited reduced growth properties in liquid culture with tetracycline and could easily be differentiated from bacteria transformed by non-recombinant plasmids. The formation of plasmid multimers increased the resistance to tetracycline at the level of the induction period, presumably as a result of a gene dosage effect.
多瘤病毒DNA的两个HindIII片段被克隆到质粒pBR322的HindIII位点，该位点位于参与四环素抗性表达的RNA聚合酶启动子中。虽然将外源DNA插入该位点并不总是导致四环素抗性完全丧失，但携带重组质粒的大肠杆菌K12菌株chi 1776在含有四环素的液体培养物中生长特性降低，并且很容易与由非重组质粒转化的细菌区分开来。质粒多聚体的形成在诱导期水平上增加了对四环素的抗性，推测这是基因剂量效应的结果。
