Rubin R A, Levy S B
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
J Bacteriol. 1990 May;172(5):2303-12. doi: 10.1128/jb.172.5.2303-2312.1990.
Inner membrane Tet proteins encoded by tet genes in gram-negative bacteria mediate resistance to tetracycline (Tcr) by directing its export. Total sequences for class A, B, and C tet genes demonstrate that their products have a common ancestor, with Tet(A) and Tet(C) being more closely related (78% identical) than either is to Tet(B) (45% identical). The N- and C-terminal halves of Tet(B) and Tet(C) appear to comprise separate domains, and trans-complementation observed between tetracycline sensitive mutants in either domain of Tet(B) suggests separate but interactive functions for these domains. In this present study, interdomain hybrid genes were constructed to express hybrid tet products whose N- and C-terminal halves were derived from different family members [Tet(A/C), Tet(B/C), and Tet(C/B)]. Tet(A/C) specified a level of Tcr comparable to wild-type Tet(C) and 60% that of Tet(A), indicating that domains from these closely related tet products can function in cis. Although neither Tet(B/C) nor Tet(C/B) hybrids conferred significant Tcr, cells producing both of these types of hybrid proteins expressed substantial Tcr, indicating that productive interactions can occur in trans between Tet(B/C) and Tet(C/B). Taken together, these results suggest that highly specific interactions between the N- and C-terminal domains are necessary for Tcr and do not occur in individual hybrids derived from the more distant relatives, Tet(B) and Tet(C). This requirement for specific interactions suggests that N- and C-terminal domains have coevolved in each member of the Tet family.
革兰氏阴性菌中tet基因编码的内膜Tet蛋白通过引导四环素（Tcr）的输出介导对其的抗性。A、B和C类tet基因的完整序列表明它们的产物有一个共同的祖先，其中Tet(A)和Tet(C)的关系更为密切（78%相同），而它们与Tet(B)的关系则相对较远（45%相同）。Tet(B)和Tet(C)的N端和C端似乎由不同的结构域组成，在Tet(B)任一结构域的四环素敏感突变体之间观察到的反式互补表明这些结构域具有独立但相互作用的功能。在本研究中，构建了结构域间杂交基因以表达杂交tet产物，其N端和C端分别来自不同的家族成员[Tet(A/C)、Tet(B/C)和Tet(C/B)]。Tet(A/C)赋予的Tcr水平与野生型Tet(C)相当，为Tet(A)的60%，这表明来自这些密切相关的tet产物的结构域可以顺式发挥功能。虽然Tet(B/C)和Tet(C/B)杂交体都没有赋予显著的Tcr，但产生这两种杂交蛋白的细胞表达了大量的Tcr，这表明Tet(B/C)和Tet(C/B)之间可以反式发生有效相互作用。综上所述，这些结果表明N端和C端结构域之间高度特异性的相互作用是Tcr所必需的，并且在来自较远亲属Tet(B)和Tet(C)的单个杂交体中不会发生。这种对特异性相互作用的要求表明N端和C端结构域在Tet家族的每个成员中共同进化。
