Collagen gene structure.

The collagens of vertebrates may be divided into three groups according to chain size and whether or not the helical domains are continuous. Present evidence suggests that, at least within one of these groups, similarity between collagens is reflected in the organization of the genes that encode them. Early evidence suggested that collagen genes evolved on the basis of exons which are multiples of a primordial building block of 54 bp, separated by much larger introns. This model of collagen gene evolution is contradicted by the recent discovery of a collagen gene with a single long open reading frame.