Diversity of the glycine/tyrosine-rich keratin-associated protein 6 gene (KAP6) family in sheep

Abstract

Keratin-associated proteins (KAPs) are structural components of wool and variation in them may affect wool characteristics. In this study, we used PCR-SSCP to analyse the ovine KAP6 family which encodes glycine and tyrosine-rich KAPs. Five unique PCR-SSCP patterns were detected in the 250 sheep investigated. Between two and five patterns were observed in individual sheep and none with only one pattern was detected. This suggests the amplicons were heterogeneous and derived from more than one locus. To analyse these heterogeneous PCR amplicons, a sequencing approach using SSCP to separate individual amplified sequences, was developed. Using this approach, five DNA sequences (A-E) representing five unique PCR-SSCP patterns were obtained. D was identical to a published ovine KAP6-1 sequence (GenBank accession no. M95719), whereas the others were novel, but the closest homology was with KAP6 sequences from human, sheep, goats and cattle. The five ovine KAP6 sequences could be assigned into three distinct groups. B and D were identical to each other, with the exception of a 57-bp deletion/insertion and a single nucleotide polymorphism (SNP) in the 3'-UTR region. These appear to be allelic variants of ovine KAP6-1. A and C could form another group, as they were similar to each other (with only one synonymous SNP), but different to the other sequences. This group appears to be related to a sheep KAP6 amino acid sequence, and represent allelic variation at another KAP6 locus (designated KAP6-2). The remaining sequence E did not show high sequence homology with either the KAP6-1 or KAP6-2 sequences, but exhibited homology with a bovine KAP6-3 sequence, with the exception of a deletion/insertion of 30 nucleotides. This suggests that E represents ovine KAP6-3. This sequence was detected in only 11% of the sheep investigated, suggesting either a KAP6-3 null allele, or failure to amplify allleles. These results suggest that ovine KAP6 is a complex gene family, that is not only comprised multiple loci, but that is also polymorphic.