A recombinant phage, SpC3, containing a 17 kb genomic DNA insert representing approximately 60% of the 3′ portion of the sheep collagen α2 gene, was evaluated by electron microscopic R loop analysis. A minimum of 17 intervening sequences (introns) and 18 α2 coding sequences (exons) were mapped. With the exception of the 850 base pair exon located at the extreme 3′ end of the insert, all exons contained 250 base pairs or less. The total length of all the exons in SpC3 was 3,014 base pairs. The length distribution of the 17 introns ranged from 300 to 1600 base pairs; together, all of the introns comprised 14,070 base pairs of SpC3 DNA. Thus, the DNA region required for coding the interspersed 3 kb of α2 collagen genetic information was 5.6 fold longer than the corresponding α2 mRNA coding sequences.
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