C-ski cDNAs are encoded by eight exons, six of which are closely linked within the chicken genome.

The c-ski locus extends a minimum of 65 kb in the chicken genome and is expressed as multiple mRNAs resulting from alternative exon usage. Four exons comprising approximately 1.5 kb of cDNA sequence have been mapped within the chicken c-ski locus. However, c-ski cDNAs include almost 3 kb of sequence for which the exon structure was not defined. From our studies using the polymerase chain reaction and templates of RNA and genomic DNA, it is clear that c-ski cDNAs are encoded by a minimum of eight exons. A long 3' untranslated region is contiguous in the genome with the distal portion of the ski open reading frame such that exon 8 is composed of both coding and noncoding sequences. Exons 2 and 3 are separated by more than 25 kb of genomic sequence. In contrast, exons 3 through 8, representing more than half the length of c-ski cDNA sequences, are closely linked within 10 kb in the chicken genome.