Like the immunoglobulinIgh-VandIgk-Vgene families, the human or mouseTCRVgene families may be grouped into subfamilies displaying>75 nucleic acid sequence similarity among their members. Systematic interspecies sequence comparisons reveal that most mouseTcr-Vsubfamilies exhibit clear homology to humanTCRVsubfamilies (>60 amino acid sequence similarity). Homologous pairs ofTCRVgenes in mice and humans show higher sequence similarity thanTCRVgenes from different subfamilies within either species, indicating transpecies evolution ofTCRVgenes. Mouse and human homologues show conservation of their relative map order, particularly in the 3' region and a similar sequential and developmentally programmed expression. When the V regions from both species were analyzed together, local length differences and conserved residues in the loop regions were revealed, characteristic of each of the four TCRV families.
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