Dystrophin is the scaffold of a protein complex, disrupted in inherited muscular dystrophies. At the last 3 terminus of the gene, a protein domain is encoded, where syntrophins are tightly bound. These are a family of cytoplasmic peripheral membrane proteins. Three genes have been described encoding one acidic (␣1) and two basic (␤1 and ␤2) proteins of ϳ57-60 kDa. Here, we describe the characterization of two novel putative members of the syntrophin family, named ␥1-and ␥2-syntrophins. The human ␥1-syntrophin gene is composed of 19 exons and encodes a brain-specific protein of 517 amino acids. The human ␥2-syntrophin gene is composed of at least 17 exons, and its transcript is expressed in brain and, to a lesser degree, in other tissues. We mapped the ␥1-syntrophin gene to human chromosome 8q11 and the ␥2-syntrophin gene to chromosome 2p25. Yeast two-hybrid experiments and pull-down studies showed that both proteins can bind the C-terminal region of dystrophin and related proteins. We raised antibodies against these proteins and recognized expression in both rat and human central neurons, coincident with RNA in situ hybridization of adjacent sections. Our present findings suggest a differentiated role of a modified dystrophin-associated complex in the central nervous system.Since the identification of dystrophin, the product of the Duchenne muscular dystrophy gene at Xp21, molecular genetics has moved quickly (1, 2). The deficiency of dystrophin in Duchenne muscular dystrophy (DMD) 1 and its first animal model, the mdx mouse, leads to a dramatic reduction in a group of previously unknown proteins identified as the dystrophinassociated protein complex.In the last few years, the dystrophin-associated protein complex proteins have been isolated; their genes have been cloned; and the following model of the complex has been hypothesized (3-5). Dystrophin is a large rod-shaped protein, primarily localized beneath the muscle cell membrane. Its actinin-like N terminus binds F-actin (6), whereas its C terminus is anchored to the transmembrane protein, ␤-dystroglycan, which is linked through ␣-dystroglycan to the extracellular merosin (laminin-2) (7). Then, this complex bridges the muscle membrane from the cytoskeleton to the extracellular matrix. In addition, dystroglycan is the receptor for agrin, a protein with a pivotal role in the clustering of acetylcholine receptors at the neuromuscular junction (8 -10) and a fundamental element of the basal lamina (11). At the muscle membrane, this complex is associated with the hydrophobic sarcospan DAP25 (dystrophinassociated protein; A5) (12) and the sarcoglycan complex, which is composed of at least four interacting transmembrane glycoproteins: ␣-sarcoglycan (DAG50 (dystrophin-associated glycoprotein), A2, adhalin) (13, 14), ␤-sarcoglycan (DAG43, A3b) (15, 16), ␥-sarcoglycan (DAG35, A4) (17), and ␦-sarcoglycan (18). Mutations in the laminin-␣2 gene are responsible for congenital muscular dystrophy (19); mutations in the ␥-, ␣-, ␤-, and ␦-sarcoglycan genes cause limb-girdle mus...

A 104-kD protein was coimmunoprecipitated with the estrogen receptor from the flowtrough of a phosphocellulose chromatography of MCF-7 cell nuclear extract. mAbs to this protein identified several cDNA clones coding for the human 104-kD major vault protein. Vaults are large ribonucleoprotein particles of unknown function present in all eukaryotic cells. They have a complex morphology, including several small molecules of RNA, but a single protein species, the major vault protein, accounts for >70% of their mass. Their shape is reminiscent of the nucleopore central plug, but no proteins of known function have been described to interact with them. Western blot analysis of vaults purified on sucrose gradient showed the presence of estrogen receptor co-migrating with the vault peak. The AER317 antibody to estrogen receptor coimmunoprecipitated the major vault protein and the vault RNA also in the 20,000 g supernatant fraction. Reconstitution experiments of estrogen receptor fragments with the major vault protein mapped the site of the interaction between amino acids 241 and 280 of human estrogen receptor, where the nuclear localization signal sequences are located. Estradiol treatment of cells increased the amount of major vault protein present in the nuclear extract and coimmunoprecipitated with estrogen receptor, whereas the anti-estrogen ICI182,780 had no effect. The hormone-dependent interaction of vaults with estrogen receptor was reproducible in vitro and was prevented by sodium molybdate. Antibodies to progesterone and glucocorticoid receptors were able to coimmunoprecipitate the major vault protein. The association of nuclear receptors with vaults could be related to their intracellular traffic.

No abstract

Mutations in any of the genes encoding the alpha, beta or gamma-sarcoglycan components of dystrophin-associated glycoproteins result in both sporadic and familial cases of either limb-girdle muscular dystrophy or severe childhood autosomal recessive muscular dystrophy. The collective name 'sarcoglycanopathies' has been proposed for these forms. We report the identification of a fourth member of the human sarcoglycan family. We named this novel cDNA delta-sarcoglycan. Its mRNA expression is abundant in striated and smooth muscles, with a main 8 kb transcript, encoding a predicted basic transmembrane glycoprotein of 290 amino acids. Antibodies specifically raised against this protein recognized a single band at 35 kDa on western blots of human and mouse muscle. Immunohistochemical staining revealed a unique sarcolemmal localization. FISH, radiation hybrid and YAC mapping concordantly linked the delta-sarcoglycan gene to 5q33, close to D5S487 and D5S1439. The gene spans at least 100 kb and is composed of eight exons. The identification of a novel sarcoglycan component modifies the current model of the dystrophin-glycoprotein complex.

No abstract