UASt regulatory sequences drive expression of comm containing mutations in the two PY motifs that are normally responsible for Nedd4 binding (carries the amino acid replacements P221A and P230A). 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.