Vectors are available for SNAP-, CLIP-, ACP- and MCP-tag fusion protein expression and labeling in mammalian and bacterial systems. The mammalian SNAPf and CLIPf vectors express faster-reacting variants of the SNAP- and CLIP-tags than previously available vectors. Improved polylinker sequences both upstream and downstream from the tag allow expression of the tag on either end of the protein of interest, under control of the CMV promoter. SNAPf-tag and CLIPf-tag expression vectors contain a neomycin resistance (NeoR) gene for selection of stable transfectants, together with an IRES element for efficient expression of both the fusion protein and NeoR. The ACP-tag and MCP-tag expression vectors are under control of the CMV promoter. The ACP-tag expression vector (NEB #N9322) is suitable for transient or stable expression but the MCP-tag expression (NEB #N9317) vector is suitable for transient expression only. Codon usage has been optimized for mammalian expression. Control plasmids encoding fusion proteins that are localized to the nucleus [(H2B) (NEB #N9186)], mitochondria [(Cox8A) (NEB #N9185)] and cell surface [ADRβ2 (NEB #N9184), NK1R (NEB #N9216), GPI (NEB #N9320)] are also available.The pSNAP-tag®(T7)-2 Vector (NEB #N9181) is an E.coli expression plasmid encoding the SNAP-tag protein. The codon usage of the SNAP26b gene is optimized for expression in E. coli. Expression is under control of the IPTG-inducible T7 promoter.