PRIMARY STRUCTURE OF THE ALPHA-1 CHAIN OF HUMAN TYPE-XV COLLAGEN AND EXON-INTRON ORGANIZATION IN THE 3(') REGION OF THE CORRESPONDING GENE

Types XV and XVIII collagens form a new subgroup within the diverse fa mily of collagens, both being characterized by extensive interruptions in their collagenous sequences. We isolated human alpha 1(XV) chain c DNAs that extend beyond the sequences previously derived from a 2127-n ucleotide clone. The cDNAs cover 5172 nucleotides of the 5300-4400 nuc leotide mRNAs and encode a polypeptide of 1388 residues, including a 2 5-residue signal peptide, a 530-residue NH2-terminal noncollagenous do main (NCI), a 577-residue collagenous sequence with eight interruption s of 7-45 residues, and a 256-residue COOH-terminal noncollagenous dom ain (NC10). A thrombospondin sequence motif found previously in certai n other collagen types was identified in the NC1 domain of type XV col lagen, whereas the NC10 domain was characterized by the presence of fo ur cysteine residues. The exon-intron organization of the human gene w as determined, corresponding to the extreme COOH-terminal 2/3 + 275 re sidues. NC10 is encoded by seven exons, six of which encode solely pro tein sequences and vary in size between 60 and 186 base pairs, whereas the last one corresponds to the end of the polypeptide and the 3'-unt ranslated sequences. The extreme 5' exon analyzed was a junction exon encoding both collagenous and noncollagenous sequences. This initial c haracterization is indicative of a multiexon arrangement for the alpha 1(XV) gene.