BirA(G3) corresponds to a promiscuous biotin ligase derived by mutation of the Escherichia coli birA gene (EcoGene:EG101230); BirA(G3) contains the following amino acid substitutions relative to the wild-type protein; Q65P, I87V, R118S, E140K, Q141R, S150G, L151P, V160A, T192A, M209V and I305V. BirA(G3) can thus be used as a proximity labeling tool for proteomic analysis; it was selected for high activity (FBrf0240093). The exact sequence of the BirA(G3) biotin ligase may vary depending on the particular transgene or modified endogenous locus being used; the coding sequence may have been codon optimized for use in different species, and amino acid residue A146 may have been deleted to suppress dimerization. For a comparison of BirA(G3) with other protein proximity labeling tools, see FBrf0240093.