Zalacain M, Cundliffe E
Department of Biochemistry, University of Leicester, U.K.
Gene. 1991 Jan 2;97(1):137-42. doi: 10.1016/0378-1119(91)90021-3.
In addition to tlrA, tlrB and tlrC, which were previously cloned by others, a fourth antibiotic-resistance gene (tlrD) has been isolated from Streptomyces fradiae, a producer of tylosin (Ty), and cloned in Streptomyces lividans. Like tlrA, tlrD encodes an enzyme that methylates the N6-amino group of the A2058 nucleoside within 23S ribosomal RNA. However, whereas the tlrA protein dimethylates that nucleoside, the tlrD product generates N6-monomethyladenosine. The genes also differ in their mode of expression: tlrA is inducible, whereas tlrD is apparently expressed constitutively, and it has been confirmed that the tlrA-encoded enzyme can add a second methyl group to 23S rRNA that has already been monomethylated by the tlrD-encoded enzyme. Presumably, that is what happens in S. fradiae.
除了先前被其他人克隆的tlrA、tlrB和tlrC之外，从泰乐菌素（Ty）产生菌弗氏链霉菌中分离出了第四个抗生素抗性基因（tlrD），并将其克隆到了变铅青链霉菌中。与tlrA一样，tlrD编码一种使23S核糖体RNA内A2058核苷的N6-氨基甲基化的酶。然而，tlrA蛋白使该核苷二甲基化，而tlrD产物产生N6-单甲基腺苷。这些基因在表达模式上也有所不同：tlrA是可诱导的，而tlrD显然是组成型表达，并且已经证实tlrA编码的酶可以将第二个甲基添加到已经被tlrD编码的酶单甲基化的23S rRNA上。据推测，在弗氏链霉菌中就是这样发生的。
