THE MESSENGER-RNA FOR ALPHA-1(XIX)-COLLAGEN CHAIN, A NEW MEMBER OF FACITS, CONTAINS A LONG UNUSUAL 3'-UNTRANSLATED REGION AND DISPLAYS MANY UNIQUE SPLICING VARIANTS

We have isolated cDNAs and completed for the first time the primary structure for a novel collagenous chain that was partially characterized earlier and named alpha 1(Y) chain [Yoshioka, H. et al. (1992) Genomics 13, 884-886]. The size of the coding region was unexpectedly small compared with the length of the mRNA (>10 kb), owing to the presence of a long 3' untranslated region (>5 kb). The predicted polypeptide contained 1,142 amino acid residues with a 23-residue signal peptide consisting of 5 collagenous domains of 70-224 residues in length, interspersed and flanked with 6 noncollagenous (NC) domains. The primary structure is distinct from those of the 32 known collagen alpha-chains of types I through XVIII. Therefore, we designate this newly discovered collagen chain the al chain of type XIX collagen. Sequence analysis suggested that this chain belongs to the recently discovered group of collagens known as FACITs (fibril associated collagens with interrupted triple-helices). Northern blotting analysis demonstrated hybridization of the cDNA to a large mRNA species (>10 kb) extracted from a rhabdomyosarcoma cell line (CCL 136). We also isolated numerous truncated cDNA clones of which the 3' parts were different from the ''proto'' type of the mRNA of > 10-kb size. Sequence comparison between cDNAs and corresponding genomic DNA fragments indicated that unusual splicing events occurred through insufficient recognition at acceptor sites. Expression of the gene was extremely infrequent in the rhabdomyosarcoma cell line; it could be restricted to certain animal tissues both temporally and spatially during early development.