| Summary: | Keratin-associated proteins (KAPs) are a diverse group of proteins and form a matrix that cross-links keratin intermediate filaments in hair and wool fibres. From over 100 KAP genes (<i>KRTAPs</i>) identified in mammalian species, <i>KRTAP25-1</i> is a high sulphur (HS)-KAP gene, which has recently been described in humans. Here, we report the absence of <i>KRTAP25-1</i> in sheep, and describe a new HS-<i>KRTAP</i> (named <i>KRTAP28-1</i>) in the chromosome region where <i>KRTAP25-1</i> was expected to be found. Six variants (<i>A</i>−<i>F</i>) of <i>KRTAP28-1</i> containing eight single nucleotide polymorphisms (SNPs) and a TG repeat polymorphism were detected. One was positioned 30 bp upstream of the transcription start codon and all the others were non-synonymous SNPs, including a nonsense SNP. The TG repeat polymorphism would lead to a reading frame shift at the carboxyl-terminal end. The effect of <i>KRTAP28-1</i> on wool traits was investigated with 383 Southdown × Merino-cross lambs from seven sire lines. Of the four genotypes with a frequency of over 5%, lambs of genotypes <i>AB</i> and <i>BD</i> produced wool of a smaller MFD than lambs of genotype <i>BC</i>. This shows that <i>KRTAP28-1</i> is associated with wool fibre diameter, and that variation in this gene might have potential for use as a gene marker for reducing wool fibre diameter.
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