Identification of the keratin-associated protein 13-3 (KAP13-3) gene in sheep

Keratin-associated proteins (KAPs) are a major structural component of hair and wool fibres, and play a critical role in determining the properties of the fibre. To date, forty functional high sulphur KAP genes from fourteen families have been identified in humans, but only seven functional high sulphur KAP genes have been identified in sheep. This led us to search for the ovine KAP13-3 gene, a gene encoding a high sulphur KAP. In this study, the notional KAP133 gene (KRTAP13-3) was amplified using primers designed based on a reported bovine KRTAP13-3 sequence. PCR-single stranded conformational polymorphism (PCR-SSCP) analysis was used to screen amplicons derived from the gene in one hundred and forty seven New Zealand Romney cross-bred sheep. Five unique banding patterns were revealed. Either one PCR-SSCP pattern (homozygous) or a combination of two patterns (heterozygous) was observed for each sheep. Sequencing of PCR amplicons representtative of different SSCP patterns revealed five different DNA sequences. The sequences derived from the amplicons showed a low homology to other known ovine KRTAPs, but had a high homology with previous reported KRTAP13-n sequences from human and cattle, with the closest homology being with bovine KRTAP13-3, suggesting the sequences represent the ovine KRTAP13-3 locus. Among the five allele sequences, four nucleotide substitutions were identified within the coding region. Of these substitutions, three were non-synonymous and would result in amino acid changes (p.Arg79Cys, p.Arg81Gln and p.Tyr130His). This variation in the KAP13-3 gene may affect gene expression, the structure and assembly of the protein, and consequently influence wool traits, if KAP13-3 is of importance to wool fibre structure.