Halo7-tag is an engineered form of a Rhodococcus dehalogenase gene (DhaA) that forms a covalent bond with chloroalkane groups. A protein fused to Halo7-tag can react with a fluorescent compound carrying a chloroalkane group in vivo, resulting in rapid, irreversible and specific chemical tagging of the protein. Halo7-tag shows increased expression, and improved stability and substrate-binding kinetics compared to Halo2-tag (PMID:23248739).