A mutated form of arm, in which amino acids 549-606 are deleted to produce a fusion of Arm repeats 10 and 11 and deletion of the insertion normally found between these repeats, 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 and to shg protein in a coimmunoprecipitation assay.