Through their involvement in the integration and excision of a large number of mobile genetic elements, such as phages and integrative and conjugative elements (ICEs), site‐specific recombination systems based on heterobivalent tyrosine recombinases play a major role in genome dynamics and evolution. However, despite hundreds of these systems having been identified in genome databases, very few have been described in detail, with none from phages that infect Bacillota (formerly Firmicutes). In this study, we reanalyzed the recombination module of Lactobacillus delbrueckii subsp. bulgaricus phage mv4, previously considered atypical compared with classical systems. Our results reveal that mv4 integrase is a 369 aa protein with all the structural hallmarks of recombinases from the Tn916 family and that it cooperatively interacts with its recombination sites. Using randomized DNA libraries, NGS sequencing, and other molecular approaches, we show that the 21‐bp core‐attP and attB sites have structural similarities to classical systems only if considering the nucleotide degeneracy, with two 7‐bp inverted regions corresponding to mv4Int core‐binding sites surrounding a 7‐bp strand‐exchange region. We also examined the different compositional constraints in the core‐binding regions, which define the sequence space of permissible recombination sites.

中文翻译：

---

重新定义噬菌体mv4位点特异性重组系统及其attB和core-attP位点的序列特异性

基于异二价酪氨酸重组酶的位点特异性重组系统参与大量可移动遗传元件（例如噬菌体以及整合和接合元件（ICE））的整合和切除，在基因组动力学和进化中发挥着重要作用。然而，尽管基因组数据库中已鉴定出数百个此类系统，但详细描述的系统却很少，没有一个来自感染噬菌体的系统。杆菌属（以前厚壁菌门）。在本研究中，我们重新分析了重组模块德氏乳杆菌亚种保加利亚菌噬菌体 mv4，以前被认为与经典系统相比是非典型的。我们的结果表明，mv4 整合酶是一种 369 个氨基酸的蛋白质，具有 Tn 重组酶的所有结构特征916家族并与其重组位点合作相互作用。使用随机 DNA 文库、NGS 测序和其他分子方法，我们表明 21 bp 核心攻击力和属性B仅当考虑核苷酸简并性时，位点才与经典系统具有结构相似性，两个 7-bp 反向区域对应于MV4围绕 7 bp 链交换区域的完整核心结合位点。我们还检查了核心结合区的不同组成限制，这些限制定义了允许重组位点的序列空间。