Conjugative relaxases are well-characterized proteins responsible for the site- and strand-specific endonucleolytic cleavage and strand transfer reactions taking place at the start and end of the conjugative DNA transfer process. Most of the relaxases characterized biochemically and structurally belong to the HUH family of endonucleases. However, an increasing number of new families of relaxases are revealing a variety of protein folds and catalytic alternatives to accomplish conjugative DNA processing. Relaxases show high specificity for their cognate target DNA sequences, but several recent reports underscore the importance of their activity on secondary targets, leading to widespread mobilization of plasmids containing an oriT-like sequence. Some relaxases perform other functions associated with their nicking and strand transfer ability, such as catalyzing site-specific recombination or initiation of plasmid replication. They perform these roles in the absence of conjugation, and the validation of these functions in several systems strongly suggest that they are not mere artifactual laboratory observations. Other unexpected roles recently assigned to relaxases include controlling plasmid copy number and promoting retrotransposition. Their capacity to mediate promiscuous mobilization and genetic reorganizations can be exploited for a number of imaginative biotechnological applications. Overall, there is increasing evidence that conjugative relaxases are not only key enzymes for horizontal gene transfer, but may have been adapted to perform other roles which contribute to prokaryotic genetic plasticity. Relaxed target specificity may be key to this versatility.

中文翻译：

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结合松弛酶的秘密生活。

结合松弛酶是特征充分的蛋白质，负责在结合DNA转移过程的开始和结束时发生的位点和链特异性内切核酸裂解和链转移反应。在生化和结构上表征的大多数松弛酶都属于HUH内切核酸酶家族。但是，越来越多的新的松弛酶家族揭示了多种蛋白质折叠和催化替代物，以完成共轭DNA加工。松弛酶对它们的同源靶DNA序列显示出高特异性，但是最近的一些报道强调了它们对次级靶的活性的重要性，从而导致了广泛地动员含有oriT样序列的质粒。一些松弛酶还具有与其切刻和链转移能力相关的其他功能，例如催化位点特异性重组或质粒复制的启动。它们在没有结合的情况下发挥了这些作用，并且在几个系统中对这些功能的验证强烈表明它们不仅仅是人工的实验室观察。最近分配给松弛酶的其他意外作用包括控制质粒拷贝数和促进逆转座。它们介导混杂动员和基因重组的能力可用于许多富有想象力的生物技术应用。总体而言，越来越多的证据表明，共轭松弛酶不仅是水平基因转移的关键酶，而且可能已被适配成执行其他有助于原核基因可塑性的作用。放松的靶标特异性可能是这种多功能性的关键。