Identification and sequence analysis of the keratin-associated protein 24-1 (KAP24-1) gene homologue in sheep

Keratin-associated proteins (KAPs) are major structural components of hair and wool fibres, and play a critical role in determining the properties of the fibre. While over 100 KAP genes that have been grouped into 27 KAP families have been identified in mammals, most homologues remain unidentified in sheep. A BLAST search of the Ovine Genome Assembly v2.0 using a human KRTAP24-1 coding sequence (NM_001085455), identified a putative ovine KAP24-1 gene clustered with six other known KAP genes on chromosome 1. The KAP24-1 gene was amplified from the genomic DNA of 260 New Zealand Romney-cross sheep and stem-loop conformational polymorphism (SLCP) analysis of the amplicons revealed four unique banding-patterns, representing four different DNA sequences. These sequences were not closely homologous with any known ovine KRTAP and the highest similarity was with KRTAP24-1 sequences from humans, cattle, dog, pig, Sumatran orangutan and northern white-cheeked gibbon. This suggests that the sequences were allelic variants of ovine KRTAP24-1. Among these four sequences, seven nucleotide substitutions in the coding region were identified and four of the substitutions were non-synonymous. The putative ovine KAP24-1 polypeptide consisted of 252 amino acids. While probably belonging to the high-sulphur KAP group, the polypeptide had a moderate level of cysteine, but a high content of serine and tyrosine. The polypeptide possesses two putative N-glycosylation sites and a number of residues that may be O-glycosylated and/or phosphorylated.