COMPLETE STRUCTURAL ORGANIZATION OF THE HUMAN ALPHA-1(V) COLLAGEN GENE (COL5A1) - DIVERGENCE FROM THE CONSERVED ORGANIZATION OF OTHER CHARACTERIZED FIBRILLAR COLLAGEN GENES

Genes that encode the vertebrate fibrillar collagen types I-III have previously been shown to share a highly conserved intron/exon organization, thought to reflect common ancestry and evolutionary pressures at the protein level. We report here the complete intron/exon organization of COL5A1, the human gene that encodes the alpha 1 chain of fibrillar collagen type V. The structure of COL5A1 is shown to be considerably diverged from the conserved structure of the genes for fibrillar collagen types I-III. COL5A1 has 66 exons, which is greater than the number of exons found in the genes for collagen types I-III. The increased number of exons is partly due to the increased size of the pro-alpha 1 (V) N-propeptide, relative to the sizes of the N-propeptides of the types I-III procollagen molecules. In addition, however, the increased number of exons is due to differences in the intron/exon organization of the triple-helix coding region of COL5A1 compared to the organization of the triple-helix coding regions of the genes for collagen types I-III. Of particular interest is the increase of 54 bp exons in this region of COL5A1, strongly supporting the proposal that the triple-helix coding regions of fibrillar collagen genes evolved from duplication of a 54 bp primordial genetic element. Moreover, comparison of the structure of COL5A1 to the highly conserved structure of the genes of collagen types I-III provides insights into the probable structure of the ancestral gene that gave rise to what appears to be two classes of vertebrate fibrillar collagen genes. (C) 1995 Academic Press, Inc.