DNA-Mimic Antirestriction Proteins ArdA Could Regulate Gene Expression in Escherichia coli

Antirestriction proteins protect mobile genetic elements from the host's restriction-modification systems. Here, we investigated the ability of ArdA and ArdB antirestriction proteins to regulate gene expression in an engineered E. coli K-12 MG1655-based biosensor strain. This biosensor strain harbors a lux-based reporter system controlled by the AllR-repressed promoter. Although structurally similar, DNA-mimic ArdA proteins interact with AllR differently. Recently described small sArdC and well-known ArdA from the conjugative plasmid R64 appear to bind AllR and open the promoter, while the other tested antirestriction proteins (small sArdN protein and various full-sized ArdA proteins from different sources) have no effect on gene expression under AllR-controlled promoter. Direct binding between ArdA and AllR was experimentally confirmed using pull-down assays with His-tagged ArdA. Our study opens up prospects for the specific use of antirestriction proteins for the regulation of gene expression. Surprisingly, ArdB, a non-DNA-mimic antirestriction protein used initially as a control, was also able to open the promoter, apparently through nonspecific interaction with DNA. We verified this effect with a distant ArdB homolog from a rhizobacterium, which was also able to open the promoter.