alpha 1(XX) collagen, a new member of the collagen subfamily, fibril-associated collagens with interrupted triple helices

Chick cDNA clones for a new member of the FACIT (fibril-associated collagen s with interrupted triple helices) subfamily have been isolated and sequenc ed. The collagen chain encoded by these cDNAs was assigned the next consecu tive number, making it the alpha1(XX) collagen chain. Assignment of type XX collagen to the FACIT family was based on sequence similarities to types X II and XIV collagen. Type XX collagen mRNA is not abundant in the chick emb ryo. It is most prevalent in corneal epithelium. It is also detectable by r everse transcription polymerase chain reaction in embryonic skin, sternal c artilage, and tendon, but is barely detectable in calvaria, notochord, or n eural retina at select stages of development, suggesting that it is not exp ressed in these tissues. The cDNA predicts that the alpha1(XX) collagen pol ypeptide is smaller than the short forms of collagen XII and XIV. A polyclo nal antibody against a synthetic alpha1(XX) peptide reacts with polypeptide bands of 185, 170, and 135 kDa by Western blot analysis. From its similari ty to types XII and XIV collagen, type XX is expected to bind to collagen f ibrils, projecting the amino-terminal domains away from the fibrillar surfa ce. The projecting NC 3 domains are predicted to be about half the length o f those of collagen XIV.