CLONING AND CHARACTERIZATION OF THE EQUINE F-18 GENE, WHICH HAS A NOVEL EXON

A genomic clone isolated from an equine genomic library probed with an oligonucleotide (CAG)(10) showed high sequence similarity to the huma n F18 gene and was tentatively named equine F18 gene. Because the huma n F18 gene is expressed in many tissues, we examined whether this equi ne clone was also expressed in equine tissues. The cDNA encoding equin e F18 was obtained by the reverse transcriptase-polymerase chain react ion (RT-PCR) from equine thymus. The nucleotide sequence of the equine F18 cDNA (1940 bp) was determined and contained both the ATG initiati on codon and a poly(A) sequence. The cDNA sequence contained sequence homologous to exon 3 of human F18 gene and a new exon that is not foun d in the human F18 gene. The equine F18 gene contains a CAG repetitive sequence (CRS) that is translated into a polyglutamine tract, The CRS was analyzed for polymorphism by PCR: four and two different alleles were observed with unrelated east-Asian and thoroughbred horses, respe ctively. The equine F18 gene was mapped to Xq29.1 by fluorescence in s itu hybridization. The human F18 gene is also X-linked. These data str ongly supported the conclusion that the clone contains the equine homo logue of the human F18 gene.