Genes encoding the horse (Equus caballus) T-cell receptor beta chain (TCRB) were cloned and characterized. Of 33 cDNA clones isolated from the mesenteric lymph node, 30 had functionally rearranged gene segments, and three contained germline sequences. Sixteen unique variable segments (TCRBV), 14 joining genes (TCRBJ), and two constant region genes (TCRBC) were identified. Horse TCRBV were grouped into nine families based on similarity to human sequences. TCRBV2 and TCRBV12 were the most commonly represented horse families. Analysis of predicted protein structure revealed the presence of conserved regions similar to those seen in TCRB of other species. A decanucleotide promoter sequence homologous to those found in humans and mice was located in the 5′ untranslated region of one horse gene. Germline sequences included the 5′ region of the TCRBD2 gene with flanking heptamer/nonamer recombination signals and portions of the TCRBJ-C2 intron. Southern blot hybridizations demonstrated restriction fragment length polymorphisms at the TCRBC locus among different horse breeds.
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