An IncC or IncA plasmid is needed to enable transfer of SGI1 type integrative mobilisable elements but an IncC plasmid does not stably co-exist with SGI1. However, the plasmid is stably maintained with SGI1-K, a natural SGI1 deletion variant that lacks the sgaDC genes (S007 and S006) and the upstream open reading frame (S008) found in the SGI1 backbone. Here, the effect of the sgaDC genes and S008 on the stability of an IncC plasmid in an Escherichia coli strain with or without SGI1-K was examined. Co-transcription of the S008 open reading frame with the downstream sgaDC genes was established. When a strain containing SGI1-K complemented with a pK18 plasmid that included S008-sgaDC or sgaDC expressed from the constitutive pUC promoter was grown without antibiotic selection, the resident IncC plasmid was rapidly lost but loss was slower when S008 was present. In contrast, SGI1-K and the S008-sgaDC or sgaDC plasmid were quite stably maintained for >100 generations. However, the high copy number plasmids carrying the SGI1-derived S008-sgaDC or sgaDC genes constitutively expressed could not be introduced into an E. coli strain carrying the IncC plasmid but without SGI1-K. Using equivalent plasmids with S008-sgaDC or sgaDC genes controlled by an arabinose-inducible promoter, under inducing conditions the IncC plasmid was stable but the plasmid containing the SGI1-derived genes was rapidly lost. This unexpected observation indicates that there are multiple interactions between the IncC plasmid and SGI1 in which the transcriptional activator genes sgaDC play a role. These interactions will require further investigation.

需要 IncC 或 IncA 质粒来实现 SGI1 型整合可移动元件的转移，但 IncC 质粒不能与 SGI1 稳定共存。然而，该质粒与 SGI1-K 一起稳定维持，SGI1-K 是一种天然的 SGI1 缺失变体，缺乏sgaDC基因（S007 和 S006）以及 SGI1 主干中发现的上游开放阅读框（S008）。这里，检查了sgaDC基因和S008对具有或不具有SGI1-K的大肠杆菌菌株中IncC质粒的稳定性的影响。建立了S008 开放阅读框与下游sgaDC基因的共转录。当含有与包含S008- sgaDC或从组成型pUC启动子表达的sgaDC的pK18质粒互补的SGI1-K的菌株在没有抗生素选择的情况下生长时，驻留的IncC质粒迅速丢失，但当S008存在时丢失速度较慢。相反，SGI1-K和S008- sgaDC或sgaDC质粒相当稳定地维持>100代。然而，携带组成型表达的SGI1衍生的S008- sgaDC或sgaDC基因的高拷贝数质粒不能被引入携带IncC质粒但没有SGI1-K的大肠杆菌菌株中。使用具有S008- sgaDC或由阿拉伯糖诱导型启动子控制的sgaDC基因的等效质粒，在诱导条件下，IncC质粒是稳定的，但含有SGI1衍生基因的质粒很快丢失。这一意想不到的观察结果表明 IncC 质粒和 SGI1 之间存在多种相互作用，其中转录激活基因sgaDC发挥作用。这些相互作用需要进一步调查。