Nikolich M P, Shoemaker N B, Wang G R, Salyers A A
Department of Microbiology, University of Illinois, Urbana 61801.
J Bacteriol. 1994 Nov;176(21):6606-12. doi: 10.1128/jb.176.21.6606-6612.1994.
Results of previous investigations suggested that the conjugative transposons found in human colonic Bacteroides species were all members of a closely related family of elements, exemplified by Tcr Emr DOT. We have now found a new type of conjugative transposon, Tcr Emr 7853, that does not belong to this family. Tcr Emr 7853 has approximately the same size as the Tcr Emr DOT-type elements (70 to 80 kbp) and also carries genes encoding resistance to tetracycline (Tcr) and erythromycin (Emr); however, it differs from previously described conjugative transposons in a number of ways. Its transfer is not regulated by tetracycline and its transfer genes are not controlled by the regulatory genes rteA and rteB, which are found on Tcr Emr DOT and related conjugative transposons. Its ends do not cross-hybridize with the ends of Tcr Emr DOT-type conjugative transposons, and the Emr gene it carries does not cross-hybridize with ermF, the Emr gene found on all previously studied Bacteroides conjugative transposons. There is only one region with high sequence similarity between Tcr Emr 7853 and previously characterized elements, the region that contains the Tcr gene, tetQ. This sequence similarity ends 145 bp upstream of the start codon and 288 bp downstream from the stop codon. A 2-kbp region upstream of tetQ on Tcr Emr 7853 cross-hybridized with four additional EcoRV fragments of Bacteroides thetaiotaomicron 7853 DNA other than the one that contained tetQ. These additional cross-hybridizing bands were not part of Tcr Emr 7853, but one of them cotransferred with Tcr Emr 7853 in some matings. Thus, at least one of the additional cross-hybridizing bands may be associated with another conjugative element or with an element that is mobilized by Tcr Emr 7853. DNA that cross-hybridized with the upstream region was found in one clinical isolate of Bacteroides ovatus and four Tcr isolates of Prevotella ruminicola.
先前的研究结果表明，在人类结肠拟杆菌属物种中发现的接合转座子都是一个密切相关的元件家族的成员，以Tcr Emr DOT为代表。我们现在发现了一种新型的接合转座子Tcr Emr 7853，它不属于这个家族。Tcr Emr 7853的大小与Tcr Emr DOT型元件大致相同（70至80 kbp），并且还携带编码对四环素（Tcr）和红霉素（Emr）抗性的基因；然而，它在许多方面与先前描述的接合转座子不同。它的转移不受四环素调控，其转移基因也不受Tcr Emr DOT和相关接合转座子上发现的调控基因rteA和rteB的控制。它的末端与Tcr Emr DOT型接合转座子的末端不发生交叉杂交，并且它携带的Emr基因与所有先前研究的拟杆菌属接合转座子上发现的ermF基因也不发生交叉杂交。Tcr Emr 7853与先前表征的元件之间只有一个具有高度序列相似性的区域，即包含Tcr基因tetQ的区域。这种序列相似性在起始密码子上游145 bp处和终止密码子下游288 bp处结束。Tcr Emr 7853上tetQ上游的一个2-kbp区域与除包含tetQ的片段之外的多形拟杆菌7853 DNA的另外四个EcoRV片段发生交叉杂交。这些额外的交叉杂交条带不是Tcr Emr 7853的一部分，但其中一个在某些交配中与Tcr Emr 7853共同转移。因此，至少一个额外的交叉杂交条带可能与另一个接合元件或与由Tcr Emr 7853动员的元件相关联。在卵形拟杆菌的一个临床分离株和反刍普雷沃菌的四个Tcr分离株中发现了与上游区域发生交叉杂交的DNA。
