A repetitive structure in the chick α2-collagen gene

We have isolated a series of overlapping genomic clones that cover the α2-collagen gene. This gene has a length of at least 38 kb and contains more than 50 exons, the largest number of any gene isolated so far. The structure of the α2-collagen gene implies that the conversion of the nuclear RNA precursor to mature cytoplasmic messenger RNA for the α2-collagen includes at least 50 splicing events (Avvedimento et al. 1980). The organization of the gene is unique because the sizes of the exons in the major part of the gene, which corresponds to the helical portion of collagen, are identical. Although the sequences within these exons vary, our data strongly suggest that the ancestral collagen gene arose by multiple duplications of a single genetic unit containing an exon of unique size.