2 FORMS OF MOUSE SYNTROPHIN, A 58-KD DYSTROPHIN-ASSOCIATED PROTEIN, DIFFER IN PRIMARY STRUCTURE AND TISSUE DISTRIBUTION

Syntrophin, a 58 kd extrinsic membrane protein, is concentrated at pos tsynaptic sites at the neuromuscular junction and may be involved in c lustering acetylcholine receptors. In muscle and nonmuscle tissues, sy ntrophin is associated with dystrophin, utrophin, and two homologs of the dystrophin carboxy-terminal region. We have isolated three cDNAs e ncoding Torpedo and mouse syntrophins. The Torpedo cDNA encodes a full -length protein, and on Northern blots recognizes a 3.5 kb mRNA. The t wo mouse syntrophin cDNAs are products of separate genes but encode pr oteins that share 50% identity. Syntrophin-1 mRNA (2.2 kb) is expresse d at highest levels in skeletal muscle. Syntrophin-2 mRNAs (2.2, 5.0, and 10 kb) are expressed in all mouse tissues examined. These patterns of expression suggest that syntrophin-1 and syntrophin-2 may associat e with different members of the dystrophin family.