Thomson C J, Towner K J, Young H K, Amyes S G
Department of Bacteriology, Medical School, University of Edinburgh.
J Med Microbiol. 1990 Mar;31(3):213-8. doi: 10.1099/00222615-31-3-213.
A clinical strain of Escherichia coli isolated in Nottinghamshire in 1980 was shown to harbour the type IIIa trimethoprim-resistant dihydrofolate reductase gene, previously identified on only one occasion, in New Zealand in 1979. The gene was identified by hybridisation with an 855-bp type III gene probe and its classification as a type IIIa dihydrofolate reductase was confirmed by detailed biochemical analysis of the enzyme product. The dihydrofolate reductase was identical in size and isoelectric point with the original type IIIa enzyme and shared similar inhibitory and kinetic profiles. The trimethoprim resistance gene was subsequently cloned and the type IIIa dihydrofolate reductase gene was localised to a 700-bp EcoRI-PstI fragment. This smaller fragment may prove to be a more specific DNA probe for the future identification of type IIIa dihydrofolate reductase genes.
1980年在诺丁汉郡分离出的一株临床大肠杆菌菌株被证明含有IIIa型耐甲氧苄啶二氢叶酸还原酶基因，该基因此前仅在1979年于新西兰被发现过一次。通过与一个855碱基对的III型基因探针杂交鉴定出该基因，并通过对酶产物的详细生化分析证实其为IIIa型二氢叶酸还原酶。该二氢叶酸还原酶在大小和等电点上与原始的IIIa型酶相同，并且具有相似的抑制和动力学特征。随后克隆了甲氧苄啶抗性基因，并将IIIa型二氢叶酸还原酶基因定位到一个700碱基对的EcoRI - PstI片段上。这个较小的片段可能会成为未来鉴定IIIa型二氢叶酸还原酶基因的更特异的DNA探针。
