UAS regulatory sequences drive expression of a synthetic linear polyubiquitin construct with Ecol\birA added at the C-terminus. Each ubiquitin chain in the construct (there are 6 copies present) has an N-terminal 16 amino acid sequence (Tag:BLRP) that can be biotinylated by Ecol\birA with high efficiency, together with a 5 amino-acid linker that provides accessibility to the tag by the Ecol\birA enzyme.