Exon/intron organization of the chicken type II procollagen gene: Intron size distribution suggests a minimal intron size

Overlapping genomic clones have been isolated that contain the α chain and COOH-terminal propeptide coding regions of the chicken type II procollagen gene. All type II procollagen exon sequences present in these clones have been identified and mapped by DNA sequencing. These include 43 exons coding for the α-chain triple helix, 1 exon coding for the junction between the COOH-terminal propeptide and the α-chain region, and 3 exons coding for the COOH-terminal propeptide and 3' noncoding sequences. With the exception of one additional intron between 2 exons coding for amino acids 568-585 and 586-603, exon-intron boundaries have been conserved when compared with genes for all other characterized genes for fibrillar collagens. The chicken type II procollagen gene differs from most other collagen genes in having introns of considerably smaller average size. The size distribution of the introns suggests that ≃80 base pairs may be a minimal functional size for introns in this gene. This size of intron may be necessary in a gene with a very large number of small exons to prevent aberrant splicing from removing exon sequence together with intron sequence.