The IncC family of broad-host-range plasmids enables the spread of antibiotic resistance genes among human enteric pathogens^1,2,3. Although aspects of IncC plasmid conjugation have been well studied^4,5,6,7,8,9, many roles of conjugation genes have been assigned based solely on sequence similarity. We applied hypersaturated transposon mutagenesis and transposon-directed insertion-site sequencing to determine the set of genes required for IncC conjugation. We identified 27 conjugation genes, comprising 19 that were previously identified (including two regulatory genes, acaDC) and eight not previously associated with conjugation. We show that one previously unknown gene, acaB, encodes a transcriptional regulator that has a crucial role in the regulation of IncC conjugation. AcaB binds upstream of the acaDC promoter to increase acaDC transcription; in turn, AcaDC activates the transcription of IncC conjugation genes. We solved the crystal structure of AcaB at 2.9-Å resolution and used this to guide functional analyses that reveal how AcaB binds to DNA. This improved understanding of IncC conjugation provides a basis for the development of new approaches to reduce the spread of these multi-drug-resistance plasmids.

^{广泛宿主范围质粒的 IncC 家族使抗生素抗性基因在人类肠道病原体1,2,3}中传播。尽管 IncC 质粒结合的各个方面都得到了很好的研究^4,5,6,7,8,9，但结合基因的许多作用已完全根据序列相似性进行分配。我们应用超饱和转座子诱变和转座子定向插入位点测序来确定 IncC 结合所需的基因集。我们鉴定了 27 个结合基因，其中 19 个之前已鉴定（包括两个调节基因acaDC），8 个之前未与结合相关。我们展示了一个以前未知的基因acaB, 编码一个转录调节因子，它在 IncC 结合的调节中起着至关重要的作用。AcaB 结合acaDC启动子的上游以增加acaDC转录；反过来，AcaDC 激活 IncC 结合基因的转录。我们以 2.9 Å 分辨率解析了 AcaB 的晶体结构，并以此指导揭示 AcaB 如何与 DNA 结合的功能分析。这种对 IncC 结合的更好理解为开发新方法以减少这些多重耐药质粒的传播提供了基础。