CLONING AND SEQUENCE-ANALYSIS OF THE HUMAN MG160, A FIBROBLAST GROWTH-FACTOR AND E-SELECTIN BINDING MEMBRANE SIALOGLYCOPROTEIN OF THE GOLGI-APPARATUS

The amino acid sequence of MG160, a membrane sialoglycoprotein of the medial cisternae of the rat Golgi apparatus, is more than 90% identica l with CFR, a fibroblast growth factor (FGF) binding protein of chicke n membranes, and with ESL-I, a ligand for E-selectin of plasma membran es of myeloid cells; furthermore, MG160, isolated by immunoaffinity ch romatography from rat brain membranes, binds to basic FGF, The gene fo r MG160 has been assigned to human chromosome 16q22-23, To characteriz e this protein further in the human, its cDNA was cloned and sequenced , The protein has a large luminal domain composed of an initial prolin e-glutamine-rich segment, encoded by an uninterrupted exonic sequence of several CAG-CAA repeats, Expansion of CAG repeats has been implicat ed in the etiology of several neurodegenerative diseases, The proline- glutamine-rich segment is followed by 16 cysteine-rich repeats that co ntain five potential asparagine-linked glycosylation sites, which are conserved in the human, rat, mouse, and chicken, The large intralumena l domain of the protein is followed by a single transmembrane domain a nd a 13-amino-acid cytoplasmic carboxy-terminal tail, which is identic al to that in the chicken, rat, and mouse, The overall amino acid iden tifies between MG160, CFR, and ESL-1 range from 88% to 95%, In several human fetal and adult tissues, three mRNA transcripts for MG160 of 10 kb, 5 kb, and 3.8 kb were identified by Northern blot analysis of pol y(A)-selected mRNAs, These transcripts may represent alternatively spl iced mRNAs of the protein or mRNAs encoding closely related proteins o f the Golgi apparatus and/or plasma membranes.