A mutated form of arm, in which Arm repeats 3-6 are deleted (amino acids 226-392 are absent), is expressed under the control of its own promoter. The protein is tagged with a Tag:MYC epitope at residue 784 in the Gly/Pro-rich region close to the C-terminus. arm 3' trailer sequences are also present. The protein produced shows normal levels of binding to α-Cat protein in a coimmunoprecipitation assay, but binding to shg protein is abolished.