CLONING OF HUMAN BASIC A1, A DISTINCT 59-KDA DYSTROPHIN-ASSOCIATED PROTEIN ENCODED ON CHROMOSOME 8Q23-24

Duchenne and Becker muscular dystrophies are caused by defects of dyst rophin, which forms a part of the membrane cytoskeleton of specialized cells such as muscle. It has been previously shown that the dystrophi n-associated protein A1 (59-kDa DAP) is actually a heterogeneous group of phosphorylated proteins consisting of an acidic (alpha-A1) and a d istinct basic (beta-A1) component. Partial peptide sequence of the A1 complex purified from rabbit muscle permitted the design of oligonucle otide probes that were used to isolate a cDNA for one human isoform of A1. This cDNA encodes a basic A1 isoform that is distinct from the re cently described syntrophins in Torpedo and mouse add is expressed in many tissues with at least five distinct mRNA species of 5.9, 4.8, 4.3 , 3.1, and 1.5 kb. A comparison of our human cDNA sequence with the Ge nBank expressed sequence tag (EST) data base has identified a relative from human skeletal muscle, EST25263, which is probably a human homol ogue of the published mouse syntrophin 2. We have mapped the human bas ic component of A1 and EST25263 genes to chromosomes 8q23-24 and 16, r espectively.