UASt regulatory sequences drive expression of comm in which all Lys residues that serve as Ubiquitin acceptor sites have been mutated to Arg residues (amino acid replacements K162R, K167R, K168R, K171R, K248R, K269R, K275R, K278R, K280R and K291R). The comm coding sequence is fused in frame with a single mutant ubiquitin moiety that cannot itself become polyubiquitinated (contains amino acid substitutions K11R, K29R, K48R, K63R, G75A and G76A) and is tagged at the C-terminal end with a triple Tag:HA tag.