SNAPf-tag is an engineered form of the human AGT (O[6]-alkylguanine-DNA alkyltransferase) gene that forms a covalent bond with benzylguanine derivatives. A protein fused to SNAPf-tag can react with a fluorescent benzylguanine derivative in vivo, resulting in rapid, irreversible and specific chemical tagging of the protein (see PMID:12469133). SNAPf-tag has faster labeling kinetics than SNAPm-tag.
