HETEROGENEITY OF THE 59-KDA DYSTROPHIN-ASSOCIATED PROTEIN REVEALED BYCDNA CLONING AND EXPRESSION

The 59-kDa dystrophin-associated protein triplet (59-DAP) is a compone nt of the dystrophin-glycoprotein complex which may directly associate with dystrophin. The cDNA encoding one component (59-1 DAP) of the 59 -DAP triplet has now been cloned from rabbit skeletal muscle. The dedu ced amino acid sequence of 59-1 DAP predicts a 505-amino acid polypept ide containing nine potential phosphorylation sites and no predicted t ransmembrane domains. This is consistent with the 59-1 DAP being a per ipheral membrane protein associated with the cytoplasmic face of the d ystrophin-glycoprotein complex. Affinity-purified antibodies against r abbit 59-1 DAP fusion proteins only recognize the lowest band of the 5 9-DAP triplet in skeletal muscle sarcolemma and isolated dystrophin-gl ycopratein complex. The tissue-specific expression of 59-1 DAP mRNA, w hich is most prominent in skeletal and cardiac muscle and is also dete cted in brain, parallels that of dystrophin but not of utrophin. Level s of 59-1 DAP mRNA are unaffected in mdx mouse skeletal and cardiac mu scles, although all dystrophin-associated proteins, including 59-DAP, are greatly reduced in mdx mouse skeletal muscle. However, in mdx mous e cardiac muscle, the up-regulation of utrophin preserves all dystroph in-associated proteins except 59-DAP. Our results suggest that the 59- DAP triplet may contain different protein species and that the 59-1 DA P may associate more specifically with dystrophin than with utrophin.