Studying gene induction of glycopeptide resistance using gene swapping

Gene swapping is a simple but effective genetic tool for characterizing the functioning of a gene, where the gene in question is known to fulfil a distinctive biological role in the cell. VanS is a sensor kinase which, in conjunction with its cognate response regulator VanR, triggers resistance to vancomycin. One of the most important questions yet to be answered in the study of vancomycin resistance is the nature of the specific ligand recognized by the VanS sensor. A "VanRS-swap" experiment between two glycopeptide-resistant Streptomyces species known to exhibit differing responses to inducer molecules can investigate whether inducer specificity is determined solely by differences between the amino acid sequences of the VanRS two-component systems present, or by inherent differences in cell wall structure and biosynthesis between the strains. Results from such experiments demonstrate that inducer specificity is determined by the origin of the VanRS proteins and provides useful circumstantial evidence that the VanS effector ligand is the drug itself, and not an intermediate in cell wall biosynthesis that may accumulate as a result of drug action.