ArdA Protein Specificity against Type I Restriction–Modification Systems

The ArdA DNA-mimic antirestriction proteins inhibit type I restriction−modification (RMI) systems by binding instead of DNA to RMI. The ArdA specificity to DNA methylation sites recognized by RMI complexes remains poorly understood; i.e., it is unclear whether a particular DNA site is mimicked by ArdA. The ardA genes were cloned from three Gram-positive bacteria: Agrobacterium tumefaciens, Pseudomonas monteilii, and Xanthomonas sp. Antirestriction activities of their products were tested against three Escherichia coli RMI systems differing in DNA recognition/methylation sites. Although similar structures were predicted for the ArdA proteins, the strong specificity to three RMI systems was observed. The results indicate that specific DNA sites may be imitated by DNA mimic ArdA proteins.