A mutated form of arm, carrying point mutations (amino acid replacements D170A, E171A and D172A) in the first Arm repeat, 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, while binding to shg protein is slightly reduced compared to wild-type controls.